I haven't taken the DAT yet, but I've found Qvault questions to be much more doable and easy compared to Achiever or Destroyer. Most of the time, when I do Achiever I wonder what the hell I've even learned. Qvault definitely boosts my confidence, and I've heard around here that their bio questions are similar in difficulty to the DAT.
Also wanted to note that Qvault does have a PAT section. It's 10 tests. They also have an RC section of 7 tests.