The original bottle set has soft straps securing the bottle (see last picture). While you can easily grab the bottle and have a life saving sip of water at a redlight or Autobahn Stau stop-go traffic, it's nigh impossible to put the bottle back with one hand. These retainers replace the straps, allowing easy slide-out/slide-back while still securing the bottle well during travel. For a couple of years I've had large diameter hose clamps doing this job and while that worked perfectly fine, it was butt ugly (and I'm not even a café poser but a hardcore touring addict).

I wouldn't recommend PLA for this. I printed mine in PETG for now. ABS/ASA might be even better, but OTOH the bottle I typically use in this is also in PET.

NOTE: This version is for ø71 mm bottle (eg. Imsdal 0.65 liter water bottles which I love because they're a good size and have a good push-pull cap. Obviously I often refill them with tap water). See also my other model for the original TRAX aluminum 0.6 liter ø73.5 mm bottle. Other diameters are easy to add, just ask me! Please note that you can't merely scale it: The ends are designed very carefully so they can barely be fitted, and then can't unmount with a bottle inside. Actually I'd be very surprised if it unmounts even without the bottle securing it.