I have both and plan to keep both. Because the ER-301 is so versatile, it could help fill a Morphagene shaped hole in your setup but at the same time, it won’t do what the MG does better than the MG and with the MG, the 301 can now fill other shaped holes.
I absolutely love the MG and always want it doing MG things. So, I’m bias toward keeping a MG. For me, the 301 will always be the magic glue module, filling in spaces and bringing things together as my system grows/shrinks.