I had them for 9 months a couple of years ago, so here's my experience with them:
They will not work if you don't wear them to school. Eventually your orthodontist may let you wear them only at night, but at the beginning, in order for them to work, you will need to wear them pretty much all the time (take them out when eating and brushing your teeth). I know it's very easy to feel self conscious, but I had quite bad teeth in the beginning anyway, so I saw it as a means to getting a better smile, so stick with it if you can.
It'll take a while to get used to speaking with them in for a while - practise as much as you can at home, but don't worry you'll get past it, although I personally took them out for my GCSE German oral, just because German can be tricky enough to pronounce usually!
Are they the most comfortable thing? Not really, but neither are regular, fixed braces, but I guess it's worth anticipating - it will feel painful, especially when you expand them (I had a little key which I'd turn in the brace every so often which widened them gradually, which is the purpose of the brace!)
Make sure you always have a case handy, especially if you're going out to eat, and make sure you clean them! (I used Retainer Brite, you can get big packs on Amazon).
I won't lie and tell you they're an absolute breeze, because they can be quite annoying, but I felt it was worth pushing through the pain of it for the sake of having better teeth down the line in a few times. You'll probably hate it at first, but if you stick with it, you'll see a result pretty quickly. Hope this helps!