it would depend on what you want out of a air ride systems . most are only a air bag with no type of dampening control. some have a double air bag so you can set it at how high you would like it to be. and the fill the forward air chamber, to stiffen up the the air bag.kind like a preloading a spring. and there are 2 that i know of Works and Progressive that offer a real shock and a air bag,
i have been riding behind my friends that have only a air bag system and seen the rear tire bounce a bit over small bumps and ripples on the road. they say they dont really notice it at all. but they do say what a smooth ride it is.but they will also say it can get a bit bouncy .
i have the Works performance air ride on my fat boy and i love it. i dont think i would put it on my K9, because there is not enough travel in the rear end to really make a difference for me. but i would think it would help a bunch if you ride two up or take long trips with it. so you could raise it up from the extra load.
now this is just my view on things. but i do enjoy a proper operating suspension .you have to living in chicago , with all the washboard ,un-level expansion joints and i can for get about the bike eating pot holes .