For those worried about collars, I can confirm that https://www.coolcatcollars.co.uk collars do come off. You can also use a luggage scale to measure the force it takes to release.
Also, whats the point of a tracker if its not on the cat?
If it do falls off (by mistake or because the quick release did its intended job), at least you now have a good starting point where to go search for the cat. Assuming it doesn't fall off the very first day, you might also have a good idea or sense of in which area the cats normally goes strolling due to the tracking feature.
Well, if your cat is one that tolerates a collar most of the time, he'll have the tracker on most of the time, which is better than no tracking at all. One of our cats tolerates a collar without any problem.
The dog GPS collars made by e.g. Whistle are waterproof, IPX8.
You might not get a cell signal under a couple of feet of water, but that much water also means you probably aren't finding the gadget even if you have a recent GPS fix.