1) The first time I put one on the springloaded click made me jump but now I am used to pressing it down for 10 secs to make sure the adhesive sticks. Feels a bit like someone has knocked your arm for a few hours but nothing more than that!
2) The advice they give you is no more that 30 mins in the water and then come out and dry. I have seen an issue with my latest one since I was home and back at the gym and pool so I put a film of Tegaderm over it - keeps it in place and just replace when I need to. Also might be worth looking at getting some sample skin tac wipes which help it adhere
3) Under clothes, no. I have had it peek out from under a polo shirt from time to time. and of course you see it plain as day in the swimming pool but honestly, I don't care.
4) Thankfully I have not yet fallen prey to the demon door frames, but I do still get freaked out by people jostling me on the underground! Some have been known to reinsert the sensor filament back into the hole if they have been quick enough, but for most it means a new sensor.
5) Find out if you can try it for free otherwise you will have to shell out for the scanner anyway. The sensors are about £100 to cover you for a month (barring accidents) and there are FB groups with free delivery codes, and of course, you will get it VAT exempt. I know that I am unlikely (for now) to have this funded on the NHS so for me I view it as an investment to help me manage my diabetes so it might be a bit steep if you only want it for three months or so.