Did it a handful of times a few years back and was good and useful feedback. Does in itself take some organising as need person to record (and remember to hit record on the camera.......). We had a List 1 judge do our prelim test.
I help a teenager with her little horse and she's done most of the competitions over the past 6 months. She finds it really useful to get proper feedback on a test (and has been doing really well - bonus ) I suggested it to her as they didn't have any transport over the winter.