We've done a couple of the holiday courses when DD was 7 - the Musical in a Day one. DD found them fun and really enjoyed herself.
The timings aren't great if you work especially as they want you there 30 mins before finish time to watch what they have been doing that day.
I would say that the standard is fine for something to do in place of childcare, but not if you are wanting to learn new skills or get any form of training. We do the SYTS theatre skills courses as well and they have been far more useful in terms of skill acquisition.
It may be different with older age groups, but for the little ones, definitely fun more than anything.