You can change out the attachments on the RO, but I'm not sure why you would want to.
I don't have the Armageddon Gear sling, so I can't directly compare. I like the RO one, as do many others, but have heard great things about the Armageddon Gear one as well. Can't go wrong with either.
Changing out the attachments was just in case you shared the sling for different rifles with different attachment points.
Steer clear from bungie slings. You're better off with a paracord sling then anything bungie (for use on firearms anyway. Bungies are probably fine for gear like bags or range finders)
You could do that, but that would get old in a hurry. Better off to buy dedicated slings for rifles with different attachment styles IMO.