Noone will be able to say, how much you will gain with using Vimax. I think an [words=https://shop.mattersofsize.com/products/sizegenetics-penis-extender]extender[/words] is only useful, if you combinate it with manual exercises.
Doing you stretching programm in the morning, then wearing vimax to keep the penis stretched and doing your girth workout in the evenening would be perfect in my opinion.
Hope this helped!