I've been using them for a couple of years, maybe 5 total orders. Some things on their site clearly show back order, it will say available in 7-10 days or something like that. Those are the ones I don't get. The items the website shows available come in a week or so. Not fast, but in my experience, no worse or better than going to the dealer.
Dealer example: I recently used the dealer for a right rear knuckle and it took 43 days to get it. Which matched what Partzilla said, available in 30-45 days (at that time).
Now it says 24-29 days.