They are based on a proven design/patent originating from John Browning and used for many years on the Ithaca Model 37..
Other than the bottom-ejection feature, the BPS doesn't have much more in common with the Ithaca than any other pump shotgun has. The BPS tends to be heavier than most due to its steel receiver (the Model 37 and the Remington Model 870 also have steel receivers but the Ithaca is significantly lighter in weight). I like the tang-mounted safety of the Browning (like that of the Mossberg Model 500) and appreciate the slick operation of the pump.
The BPS is my favorite pump shotgun but it's a little on the heavy side for much of the upland hunting I do. Mine is pretty much relegated to waterfowl duties. The excess poundage that makes it a chore to haul all day through grouse and woodcock thickets is an advantage when soaking up recoil of heavy goose loads.