I received my repayment from them, but they are useless.
I applied for a repayment for the tax I paid two years ago, sent them my p60, they did not even use it. They just showed HMRC that bit of the form where you sign that they have authority to act on your behalf, then all payments from then were to be sent to them. So payment that was owed for this year, which was a fortune, was cut without me even knowing. They then sent me a letter saying that if I wanted payment for previous years I would have to send them the calculation. So basically, they are just cheque clearing company.
If you registered with them, be careful and tell the HMRC you are in charge of you tax, otherwise, it will be on their system that cheques are automatically sent to the Agency. I lost nearly 300 pounds for nothing. But now that I told HMRC, they are sending me cheques by the post with no delays whatsoever. You only need to contact them by letter or through the website. Whereas the Agency will only send you a basic, rubbish letter, which isn't even signed or printed properly and will only actually waste time with you when they see you are a reliable source of money.
Good luck.