Very good for being seen - can't see without street lights with the Frogs only, mind.
The silicone on my first set lasted about a year, because I was constantly moving them to another bike.
Guess if you leave them in place the silicone won't rip, it's like a rubber band.
Theyre a good minmal/backup light but not bright enough to light up the ground at all, and the new "strobe" ones are 2-3 times brighter than the old knog frogs. Ive got a pair of the old ones on my helmet at the moment and theyre decent enough for that, but i dont think id use them on their own. Theyre also very small so if you get them the same colour as your frame you can probably get away with leaving them on it 24/7.
I have a knog beetle. It was bright and convenient for my pub bike - not bright enough to work on unlit roads, but good enough to be seen in town. But now after owning it for probably about 10 months it seems to be in the habit ofrapidly draining batteries all of a sudden - like it's drawing power when switched off, so am getting a different light.