going over axel cuts down on your lift and pending on what size bag it can hurt your ride quality
putting the bags on link gives you alot more lift and a smoother ride because your bags are on your 2 lin suspension, so there is more cushing or more give-
as opposed to an over axel where the bottom plate is right on top of the rear end with no cushing and straight to the top of with notch with no cushin...
Bags on axle dont limit your lift, i had that set up on my yota and got A LOT of lift it depends on where you put your brackets, and as for ride quality, its pretty good, as long as you have shocks, mine rode like factory
more cons than pros I could go on and on....in the end....4 link is just the safest, most secure, best performing way to do it. Being cheap and 2 linking is definately not to go. I mean really...in the end, a 4 link will be cheaper than the repairs you have to do from the 2 link failing.