DS13 got twin blocks in June. He had quite a lot of pain for the first day but none at all after that. He developed a sore inside his lip which he treated with salt water, Bonjela, dental wax and painkillers and it cleared up in a day or so. There was also dribbling and slurping, but that stopped pretty quickly too..
He was told to take them out for toothbrushing, eating and swimming, and for sports that require a mouthguard.
He starts at a new school next Monday and I suspect is a bit apprehensive about his speech, luckily he'll have lots of friends from his old school with him to provide support.
He started with a 15mm overjet and now he can push his lower teeth quite far in front of his top teeth. His profile has completely changed too, he looked instantly older as soon as he put the braces in. He was told he would need them for 9-12 months, then 18 months of train tracks. He's obviously not loving the treatment but they are so effective he's really glad he's doing it.
There is an excellent longrunning thread here somewhere that I read for info and tips. One poster shared photos of her DD's amazing progress which you might find encouraging.