I like the Axa beam on the 50 version, it's a good combination of length and width. Well I feel better about using it on a cycleway because it has a top cut off, so I know I'm not frying the eyeballs of people coming the other way. I would like a high beam switch however, so I could dazzle all the morons who think "I don't really give a stuff about anybody else, I'm gonna mount this mountain bike like that glares everywhere and then brag about how bright my light is". Instead I have to reach over the bars to twist the light up and into their eyes.
The mount does need to very tight, way tighter than you think it would be, being made of plastic otherwise it'll move. But it doesn't seem to bother the light being that tight. The USB socket is waterproof with the cover on. I'm not sure how you could have it waterproof with the cover off, as there is no standard for waterproof USB plugs in use. The plugs have a seam and etc where water could penetrate and cause electrolysis of the contacts. I think the manufacturer is just covering their butt. I guess you could fill the socket with silicone grease if you wanted to use it in the rain.
I two, one each on my and my partners touring bike. I paid $50 for one and $100 for the other. The USA seems to be really expensive for dynamo lights.