Speaking from experience having worked for a few agents over the years, I would say that SubservPro/Mayday Employment are good.
I would also go as far as saying that most agents are good. There is nothing that really makes Subservpro stand head and shoulders above any other job finder.
Like all other agencies they will:
1. Pay you as little as they can, whilst charging you out at max.
2. Try to hitch you up with companies to rake in a finders fee if the ongoing work is lean.
3. Try treating you as more of an employere than an contractor.
4. Back away abruptly as soon as HMRC investigate your tax returns, denying any employer liabilty, unless you are PAYE that is.
They do pay every two weeks if memory serves me correctly…which IS good.
Make sure like using any agent that you check ALL the small print.
The REAL answer to your post as far as ongoing work would be to speak to a few Ops managers, see how they rate them and the quality of their ‘on the books’ guys …now THAT would be interesting 💡