Since we are all offering opinions here
I believe the double first base is a waste of time and effort. A fielder is still permitted to track an errant throw into the path of an unsuspecting runner with no penalty per se.
I do believe it makes it difficult for veteras which had to make an adjustment from the single base. The double base widens the frame of the play slightly and withont practice can bother some umpires.
If you want the environment to be safe at 1B, teach the players how to play the position. This is not being done AT ANY LEVEL on a consistant basis. I don't know if it is laziness or the players just cannot adapt, but there really is no excuse for it.
A properly trained F3 NEVER places any part of their foot on top of the base when receiving a throw as there is no need to touch anything, but the side of the base.