Havent used them myself, but know a few people who have.
tbh for all the bad press they get iv never thought there that bad, yes they charge silly high APR, but so do all of these types of loans, your not meant to repay over years or months your meant to repay over days maybe weeks. when my mates have used them in the past they have borrowed £100+ for a few days, maybe a week (untill pay day) then when they have paid it off they only paid an extra £10 or so on top of the money borrowed, which i dont think is too bad.
however i do agree that the fake law letters is a bit too far.