First thing don't be scared of Princeton review
Yes there is some flaw in their algorithm.
I tried their diagnostic test with no preparation at all ( completed quant in 30 mins! )
Scored : 630
Quant : 33 out of 37
Verbal : 27 out of 41
Then after a preparation of 2 months with the following scores:
GMAT PREP 1 : 750
GMAT PREP 2: 720KAPLAN
6 TESTS : 740,720,740,720,700 (This one sucks)VERITAS
I again tried princeton test:
Score : 640
Quant : 34 out of 37
Verbal 31 out of 41
Though Quant was easy 2-3 question are really hard no way (45 /51)
and verbal was of normal difficulty.
I know after reviewing carefully that I deserve greater than 640 for this attempt.