For adult pupils who are very nervous, who categorically won't do exams, or who want to try something out before a 'proper' exam, then the AB Performance Assessment is very useful. The choice of repertoire is entirely up to you, and I usually reckon you can get in 4-5 pieces in the 15 minute slot. The examiner produces a written report which you take away afterwards. Some like to chat at the beginning to find out what sort of feedback you're looking for, and all are very encouraging. They are certainly worth the money in my opinion. Everyone who I've entered for the Performance Assessment has gone on, of their own choice, to do a 'proper' exam in a future session - for most it was the reassurance of an indpendent person which was needed more than anything else.
I have used the TG Certificate exams once, and it was a disaster. To me, it is still unclear what is expected and what levels they are pitched at, and I know others have found this too. I've always felt with TG that these exams are a bit of an afterthought and despite countless revisions, have not really been thought through.
Like the Peformance Assessment, I have also used the LCM Leisure Play exams a lot, mostly with adult pupils. These are effectively a 'normal' exam, but requiring just the performance of a set number of pieces. Usually, some of these can be from the syllabus, and some can be free choice. They are marked the same as the graded exams, and unlike the the Performance Assessment, it is a pass/merit/distinction/fail assessment. I generally use these exams for pupils where their nerves are OK, and they want an independent assessment of their progress - particularly adult pupils who just learn 'for fun'. Again, all these experiences have been very positive. Obviously, with work on the supporting tests, I would have no hesitation in entering a Grade 8 Leisure Play candidate for a 'normal' Grade 8 exam as the performance standard expected is the same. There was a good article on the Leisure Play exams in a recent issue of the LCM Forte magazine http://www.uwl.ac.uk/files/LCM/lcm_exams/f...orte_2010_3.pdf
Again, I think the Leisure Play exams are very good value. Although there has been criticism of the name, I have only ever come across this criticism on these forums, and it has never bothered me or any of my candidates.
In the end, it depends what you want to get out of it. But overall, I'd say the AB and LCM options are useful and good value, and for all my candidates, have been a positive and pivotal experience.