I took it about 5 days before my real DAT and got:
19bio/23gchem/25ochem
my real thing was:
21bio/21gchem/23ochem
I really pushed bio hard at the end (probably explains the slight increase) so I'd say the real thing is certainly harder but it's not like night and day or anything. It's still helpful and gives you an accurate representation of how the questions are asked. No practice test is perfect and this is no exception, but it's not a terrible indicator like many make it sound.