I originally purchased a larger size for my wife, but it didn't fit her small female frame (just barely didn't fit). This size fits perfectly!
I wanted a bottle I could use for energy drinks, to supplement the water reservoir in my pack. This bottle fit perfectly on my 2018 Rocky Mtn Altitude and it is super easy to remove for a drink and then replace. Doesn't fall off, as tested on some very rocky mtb trails. And, the cover for the nipple keeps it clean; no trail dirt to drink. I don't plan to use the bottle on all rides, and I like the fact that the bracket on the bike is unobtrusive -- no large metal bottle cage. Perfect.
I bought the 590 bottle and base for my 2021 Small Kona Process 134, prior to purchasing the bottle system I printed out the bottle fit template for the 590 and it fit with room to spare, but when I got the 590 installed and tried to snap in the bottle, it did not fit (granted the frame space is very limited) so I tried a different bottle lid and that just barely fit overall, the bottle system was a good product with misinforming sizing.
I like longer rides when I have the time and log ~5k miles per year on my road bike. Some rides I have a half-frame bag that makes it difficult to pull a bottle up and out while on the pedals, but Fidlock's design allows for most any angle of approach and can be done without looking. Get close and 'snap'! you're in, and best...you know when you're in and can confidently return your focus to the pedals and the road. Love the squeeze bottle design which is similar to Purist bottles that I own and like. As a roadie, I removed the protective nozzle dust covers for weight and drinking convenience. They'd make sense if you're rolling around on gravel or dirt, so I welcome that consideration. They pop off fairly easily with a pinch and pull, but would easily remain attached on the roughest of roads. The overall aesthetic (and aren't we all a bit sensitive to gear-ppearance) is great and very in line with my bikes look. When ordered, I was a little sensitive to how high off the frame they'd sit with the innovative locking mech, as I have a small frame triangle, and have one bottle on the down tube and one on the seat tube, and stoked to report that they don't interfere with each other. Overall, I'm sold...these are a great addition to my ride.
Great design and bottle