We have them and they're useless. I have tried to use them several times; they charge too much, take far too long, and produce no positive results. "Well we spent a week looking at it but can't figure out what the problem is. Here's your bill." Never again.
As I type this I am examining my downloads folder on my main system, weeding out some things I don't need. I'm looking for one item in particular that concerns me but I haven't found it yet. I doubt that deleting it will make any difference but it'll make me feel better.
Edit - Item found and deleted.