Spent mine at my local VW Garage. Was pretty decent;
After the first half a day, the guy supervising me realised I was fairly competent and just left me in charge of doing the MOTs (occasionally coming past to check I hadn't ruined any cars

)
Got 2 brand new unregistered Porsche 911 GT3s come across from the Porsche garage across the road because they didn't have MOT testing facilities for PDIs and MOT checks.....and then we took them out for a bit of a spin afterwards just to check they were working all correctly
That said, we didnt half have enough Golf MK5s to MOT! Could have done one with my eyes shut by the end of the week!
Did get to try a hand at some other stuff while I was there (not just MOTs).
A good experience