I liked the idea of being able to mix water and my electrolyte as sometimes I want one or the other, or to change the strength of the electrolyte. At first I struggled to use the MXXY as it wasn't really compatible with my existing Nathan hydration pack. I waited for a sale and bought a simpler pack of a different brand that seemed to fit the MXXY bladder well. The MXXY zippers were hard to open the first time but the instructions did warn about that. They were much easier to open after the first time. I found the pouches a little tricky to fill when they were separated since they are smaller than a full bladder and don't balance as easily. Once I got everything filled up and assembled I took the MXXY on a long run. The mixing valve worked as advertised but it was not easy to use while running. Might be easier while cycling. I'm giving the MXXY 3 stars due to the excess weight of the double tubes. I found that weight annoying while I was running as the double tubes were hard to secure and they seemed to get in the way of my arms and shoulders. I'm guessing the MXXY works best with the MXXY vests but since I already had a vest or two I didn't want to buy another.

I’ve got about 10 hours of running with the 1.5 liter version so far so feel comfortable sharing some thoughts. First off, I’ve been experimenting with higher levels of carbohydrate fueling on longer runs and this is really an innovative way of supporting that. I have a 1.5 liter camelback pack that I’ve been reluctant to use with anything other than water due to cleaning challenges. The Moxxy solves this and the duel bladders allow me to mix a concentrated fuel pouch and then control the release/mix with hydration. This works really well. Still, there are a number of things I think can be iteratively improved upon. I’m not sold on the use of zippers. They work better than I thought but the zipper connecting the two bladders adds too much length/bulk to fit well in the camelback pack I have. Using a Moxxy pack maybe solves this but I suspect adds unnecessary length/weight to the pack. The bladders themselves are water tight but filling and closing is a bit of a juggling act. The tubes and dial mechanism are a tad bulky and I’d like to see these streamlined a bit more. Some other considerations include the product packaging which is nice and feels quite premium though I’d sacrifice some of that for the sake of the environment or to bring down costs as the pricepoint is probably on the high side for this product. The system itself gave off a chemical taste which was quite unpleasant but has gone away with subsequent washing and uses. And lastly, there was some unexpected shipping delay on ordering and customer service never responded to inquiries. All these things bring my rating down, however, I’m generally pleased with the product, it works as I need it to, and I would probably reorder again—particularly if the product improves on the above in future versions.

I’m a Mountainbiker and Gravel-rider and racer. Purchased the 1.5L system.
Summary: Would I recommend this product or purchase it again? No. Would I use it in races? No.
1. The dial is sensitive and when you are not making sure, that the inside plate is pointed correctly, the system will leak all over the place.
2. The system will fit fine with my USWE Nordic 4L winter pack, it will barely fit with my USWE 2.0 race pack.
3. Dial is in wrong direction to Zippers, not easy to refill.
4. Hose kinks easily, not able to roll up at all.
5. Price point: $99 is too high IMO for a system with a lot of flaws.
6. Customer service: Not very responsive

Purchased the 1.5. Honestly I like the concept but in its current state it’s extremely bulky.
It really didn’t fit in the reservoir area of my packs (zygos and Nathan, didn’t try the bronco or momentum) without effort. Compared side by side it’s larger than my 2L bladder. Hose is a bit short and the dial is bulky, it blocs access to front pouches.
I could see using this for shorter long runs and trail races but nothing where I would need to refill at an aid station as its hard to get in and out of the pack unless I give up the main compartment for ease of access. You cannot refill this without removing from a pack. I probably could use it for longer distances if I put the water on top and just refill it with a super concentrate in the bottom.
Not sure of the longevity of the zippers and again take a bit more time and time is precious at the aid stations.

Overall I’ll give it a 3 (2.5) . I like the idea but it’s just not there yet in terms of accessibility and bulkiness.

I really like this pack and the concept. I like to use my nutrition in a concentrate so this is perfect. I used it for a 2 hour mountain bike ride with high fructose and water. I set the dial at a 50/50 mix and it worked as advertised. It was super easy to fill as well as clean so that was great as well. The only issue I see for myself is that I probably wouldn't be able to adjust the dial accurately while doing certain rides, more user issue than the pack. Overall a solid 4.5 out of 5.

So I've been testing out this Flexx 1.5L Hydration System on my longer gravel rides... and honestly it's pretty cool. The whole dual-bladder thing is super handy - I can keep water separate from my electrolyte mix which is exactly what I needed. It fits great in my slim backpack without adding much weight or bulk, and I love that I can just keep plain water in my bottles (if I even bring any) while still having plenty of electrolyte mix in the bladder too. The dial makes it easy to switch between water, mix, or blend them together depending on what I'm feeling during the ride... definitely comes in clutch when you're hours into a long gravel adventure and need to change things up. Nothing fancy here, just a practical solution for anyone who gets tired of choosing between carrying water OR electrolytes on long rides. It's light, fits well, and does exactly what it's supposed to do... can't really ask for more than that.

I purchased the 2.5L bladder, and I don't love it. I like the concept, but it can be improved. First, the top bladder is only 0.75L, while the bottom bladder is 1.75L. I'd have preferred 1.25 each. The obvious hack is to put a concentrated solution in the top bladder, but because that concentrated solution has to be drawn up a fairly long hose, it can't be too thick. So I'm still going to have to stop frequently and add more Infinit to the top bladder. Second, the hose attachment is fairly heavy, because it's not just one hose but rather three hoses and one thick dial. If I'm backpacking and want to shave every last ounce, I'm not bringing this. Finally, attaching the hose to the bladder isn't easy, because first the bladders have to be filled and inside your pack, then you thread the hose attachment from front to back through the hole at the top of your pack, then hook the hose up to the bladder when it's already inside your pack and you can't see the connections very well.

I bought this 1.5L bladder recently. I have only been able to use it once so far- because of the weather- on an outdoor ride (I hope to use it on long runs as well and for MTBing). It does exactly what it says it will do. I am still getting used to how it works, but I can see that it will be great. Ease of cleaning is one of its best features, but it is pretty cool that you can get different mixtures of your liquid fuel (I love my Infinit) and water. I also had a question for the folks at mxxy about shipping and they were pretty quick to respond. Good customer service.