These are my comments for V-study Material:
- Very bad impression
- Very Old questions
- No explanations, only answers
- Some errors in the answers
The GMAT is changing, more probabilites, combinations, permutations, bold face questions...
I will say those materials are good to use like an additional ressources, but today material such as Kaplan, PR and the OG are much better because they have answer explanations which helps us to track more our errors and to analyse every mistake. If you have time, I will attack V-study and GMAT plus, but in my own point of view, working with OG, Kaplan and PR is enough to provide the score that you want....