I used to think Gridiron Authentics was legit but now I don't know. I also don't know anything about individual player stickers like Joe Montanta and Jerry Rice
Michael Irvin mini helmet with "Playmaker" inscription - Gridiron Authentics
I have the same feeling for Gridiron - i used to buy some things as I know they've had many signings in the past, mostly with NE teams like Patriots and Red Sox. My only concern is that they seem to pump out a seemingly never ending supply of the same autographs. It's possible they just have a legit huge inventory, but over the last year or two, that has been my hesitation with them.