it depends on what you want it for really. If you want a practice test, its a good choice (pushes you to your limits, with a slight side effect of destroying confidence).
If you want a reliable measure of how ready you are, look elsewhere.
If I had to study for the DAT again, I would probably buy the 3 test version (instead of 5). Its a good motivator to work harder (hah) and to be honest, a practice test is a practice test.