I used to use them a lot and they used to be great - I'm sure they still are. The best bit is that you get your prints back on real B&W paper, used to be with a nice white border too. Excellent service, fast, very nicely packaged.
I've also found them excellent...clean, well-balanced prints, negs sleeved and all returned in a card storage box. And the cost of the mailers includes postage, both ways.