The whole system isn’t cheap and you do need dedicated water bottles, which aren’t cross-compatible, but I think the Fidlock Twist system is fantastic.
I tested the excellent Fidlock bottle cage about a year ago – it’s a magnetic cage with a dedicated bottle that just twists in and out. The cage part is called the Twist Bike-Base and it attaches to regular bottle cage bosses, but Fidlock also offers a Twist Uni-base, it has the same magnetic interface but you attach this to a frame tube using two straps; you don’t need frame mounts.
It’s handy for bikes that don’t have a lot of space but I’ve actually been running this on an e-bike. Some of ebikes have bottle bosses, but a lot of the best electric mountain bike designs don’t, and that’s because they have a battery inside the down tube and there’s no space for the mounting hardware. This is the situation on the Moustache Game8 bike I have on test – the down tube is pretty small and the battery is really close to the surface, so if I want to run a bottle the Twist Uni-base is the only option.
Fitting the Twist Uni-base was a little bit tricky because the straps are only adjustable from 28 to 62 mm (Fidlock should make some extra-long straps for e-bikes) and I had to pull them through with a pair of pliers. Once installed it’s pretty secure, although I would recommend fitting the little bit of tape included as it protects the frame and also introduces a bit of extra grip. Overall, it’s secure, lightweight, low-profile and means you can get a bottle on a bike with a massive down tube.