I don't recommend them. I've won two free query package critiques via Twitter from supposedly reputable services. Both of them told me my query for Anchor was a scrap and redo. Their opinion was based on the fact that my query letter didn't fit the specific formula they use for queries, and that's my assessment of them overall--a rigid and formulaic approach.
I send that query to Query Shark and she said the complete opposite--that it worked and did its job. Lit agent > random query experts imo. Actually, Janet Reid herself and other lit agents probably do make good critters. Really just anyone who actually works in the industry or has worked in the industry, will probably be good. The people I'm dubious of are "writing coaches" and indie editors who don't have much actual experience with the trade side of things.
Final point--I really think the crits you can get on Absolute Write are banging, and totally free of course
I've had much better help, the best help in fact, from QLH forums. I would credit AW with teaching me how to do query letters. (Also, AW's opinion of my query letter aligned with the Shark's, so they're on the same page in that sense.)