Oh wow, I would never shave my underarms, that seems like a lot of additional work. For some weird reason, I have no problem with hairs there compared to the leg hairs. But my underarms are usually more tanned and the hairs bleached a bit from the sun, so they're actually not very visible.
Only 15 min hot water for showering?

I wouldn't manage to wash my hair that way :D
If it only lasts a few years, that kind of makes the investment even less appealing... Although probably if fewer grow back you'll need fewer treatments the second time if you have it done again.