These guys are peddling a loan scheme. They pay some income via an umbrella in England and Wales, but then loan you the remainder from one of three companies in the Isle of Mann. From their email to me:
Join one of our recommended Umbrella Companies and get Perkbox Gold Membership totally Free
Earn up to 500 Pounds just for referring a friend
We do not charge Any fees to the contractor ever.
Nothing legitimate here at all - apparently been at it 8.5 years with no trouble from HMRC.