I also trained with millenium and thought that my constant lifting was down to my prep but I have recently bought NSI attraction and have had no problems with lifting, I assume it must have been the product.
I found millenium good to train with as it slow setting giving you chance to correct any imperfections, but I will not be using it again on clients. NSI are more expensive initially but cheaper in the long run as you dont have to keep re-doing clients nails for free!
Just to mention also that many geeks also recommend Creative, I could not afford the course and have not trained long enough to do the conversion course.
Hope this helps x