Went to the gun show in Buffalo (Clarence) today and got my first USGI mags. They are Adventure Line 20 round. They have a metal follower. Any problems with them and if so can they be replaced with the Green Followers?

i've never had any problem with mine at all, put a LOT of rounds through mine.
if they look good, don't worry about them, it's the black plastic ones that were the problem, the alloy ones, generally worked well.
if you do replace them with green ones, be aware that you will have to make some mods to the follower to allow the full 20 rds to be loaded (shortening the follower legs)

personally, try em, if it ain't broke, don't fix it!!!!

They seemed more solid and even than the plastic followers. They only had the black or metal so thought I'd try them.

The alloy followers are generally considered the best follower for the 20 round mags.

You can make a green follower to fit but it takes work and in the end you haven't gained anything. Stick with the alloy followers.