No, The Marui M870 isn't super inefficient nor does it eject shells, it's very good. It uses the Tri shot shells.
DE AEG's are quite bad, but they got the Trishots right. I use the DE M56C, it was purchased second hand, the previous owner did some work to it: He added a rail on the bottom of the hanguard so I can use different grips, and he added a rail onto the receiver. Does make it a lot better aesthetically and the grip helps with pumping the shotgun.