dd did ABRSM last time, but performed badly on the scales and the aural (was not used to this being done on a real piano). Yes we are considering the Trinity grades as an alternative especially since it includes transposing which is a useful skill for a trumpet player.
Trinity Certificate exams are 90% performance based (10% on programme/presentation). I think they're good for students who don't do so well at the supporting tests in exam situations but I still insist that my students prepare for the supporting tests at a similar grade level as they're necessary for technique and musicianship.
My opinion is that the certificates are harder to do well in than the grade exams. For example the advanced certificate is playing grade 8 pieces but many people use it as a preparation for moving onto diploma level exams and I think it is marked more rigourously than grade 8.
A downside to the certificates is that a lot of people have no idea how they slot into traditional grade exams so may not be aware that an intermediate certificate is c. grade 5 level and an advanced certificate is grade 8 plus.
Does your DD's teacher do ABRSM or Trinity grade exams? If it's ABRSM then the scale requirement is often ridiculously onerous. Trinity has fewer scales and more sensibly chosen (IMO) so Trinity graded exams could be an option if she's only done ABRSM previously. Trinity's aural tests are also far more sensible and have no sight singing which a lot of students find difficult if they're not confident singers.
Any parents or music teachers out there with experience of these certificates rather than the traditional grade exams. dd's instrument is the trumpet but in her last exam she did very well on playing the pieces but was not very confident in the aural or scales. This seems to be a good alternative that plays to her strength i.e. actually playing pieces. Teacher has recommended grade 4, but would this Intermediate certificate be better?