Yeah, I have used them, but it was a handful of years ago, almost entirely for county histories. You made me go look at their content now and I would be hard-pressed to find they having added anything since I used them, but it appears they have raised their prices?
I didn't find them useful except to check off sources I researched and found nothing. (As you know but others might not, in genealogy it is important to track all sources checked, so you don't go back and cover ground you have already gone over.) However, I was looking for family history, not general history.