i have taken recently the Veritasprep 7 mock test .
They offer good deal time to time, so keep an eye on your mailbox or gmatclub flashboard.
I got them in $10.....wooohoo..!!

I like their test analysis part that shows as per the difficulty level, time taken for easiest to difficult.

Thats really great to have analysed your preparation.

You can cross verify your analysis with given explainations but i would really like to raise a point that in some question i found their analysis a bit confusing... so better use examples in place of wordy explaination ( a suggestion from your subscriber)

But it is must to have during your gmat prep.