I have two of them in use in addition to my regular metalic (two Rockchuckers, a Piggyback and an Ammomaster) and shotshell benches (couple of Hornady 366's).
Have a Rockchucker (for depriming) and little Lee (for bullet sizing) bolted to one, and the other I use for clamping single stage shotshell presses and clamping my case trimmer which is mounted to a piece of wood.
Easily moved and mobile, can take it along on trips in the motorhome and use out on my makeshift ranges. Also make a great toolhead for other little projects and buy extra Accrobins to slip onthe side to hold stuff and provide an extended stabilized working surface when covered with a piece of plywood.
Never tried to mount a Piggyback to one, but I would think it would bee too high and unstable. Other than that I haven't had any problem with stability and the mobility of it easily makes them worth it.
Keep an eye out as Midway periodically has them on sale and only for a few dollars more than what it cost JB to build one.