Very close to the actual GMAT

I have personally taken the GMAT exam twice and have always found that the real exam experience is very different from the ones found otherwise. However, I found the GMATClub tests to be very close to the actual experience.

Firstly, the UI of the test is very close, if not identical, to the original GMAT test UI. This will not only ensure that the user is accustomed to how to the use the interface in the actual test.
Secondly, the questions (especially quant) are very similar to the ones presented in GMAT. The questions themselves are not very long or complicated, as in some other tests, but are tricky - just like you would expect in the GMAT.
Finally, The sheer volume of the tests is amazing.