Hi Guduna,
Welcome to the GMAT Club

Well Yes
Manhattan Gmat tests are good no doubt.the quant part of
MGMAT tests is bit harder rest its the next best tests available for GMAT preparation.i will advice to not just simply buy
MGMAT tests.Buy Any one
MGMAT book of ur likes its 26$ and u may get some discount on it ..
MGMAT tests are free with purchase of any
MGMAT book..while the test seperately are available for 39$
Good part is explaination of tests with answer is gr8!!
MGMAT SC is Gr8 If u dont have it rest u can see for number properties or any other.
Apart for
MGMAT the other tests if u wanaa try is 800 score tests they are also good.
If u specially wanna focus on ur quant section for good 700+ level questions u can try
GMAT CLUB tests ...
Also apart from all this u can take one diagnostic test free of knewton,veritas,kaplan

...although these dont offer their full practice tests seperately...

I hope it helps u!!
thanx
sandy