for how long is the filter good for? (ie, how many times can you use it, assuming it doesn't get totally clogged; and if it does get clogged, can you rinse it out?...sorry if this is a stupid question!)

Is this pre-filter adaptable to polar bottle? Thanks

It's a Nylon screen that is removable, so it can be rinsed out and reused endlessly. The number of uses between cleanings depends upon how much debris there is in the water you are filtering. Just to clarify for everyone, the blue part is not a drinking spout, it is an air vent. This cap is only made for filling water bottles, not for drinking out of them.

Not a dumb question perfectly fine... The filter should last a very long time. You really cant put a finite time frame on it. It is analgous to a metal coffee filter that you use over and over again. Really as long as you clean it from buildup and dont break the micron screen this will outlast most of your other gear