We've had to use them before - absolutely awful to figure it all out
Also, when you submit your fee - even in the bit about +VAT, actually ADD 20% to whatever your fee is (eg, £300? Say £360. If it's £500, say £600, £2000? Well, £2400 innit??) - they will pay you EX VAT no matter what you've put in. So, add the VAT on top of your fee so you get paid what you actually want.
It is DEFFO set up for casual staffing, like bar staff, waiters, cleaners, agency staff etc. It is NOT designed for bands to be paid for gigs at all.
Good luck with it all!