Tm ngrs m4 system is still a worth while investment. My main niggle is that the box can lock up on semi. This can be sorted by installing a mosfet, though I have still encountered this after installing one, but if you don’t know what your doing, this can cost another £250. I have wondered if a more torquing motor would sort this?
Kwa do a nice series but I believe they have withdrawn the stop on empty feature, but have heard they are more robust than TM.
The other niggle is that the “recoil” on these is not really recoil. Effectively the feedback is the opposite to “ recoil” but precooking can help with this, but again you need and expensive mosfet and the means and knowledge to install and program.
Most other ebb are just a mock reciprocating bolt with no noticeable feedback.
I don’t really use my ngrs, it’s an expensive backup, as I prefer my gbbrs; if you are interested in these, look at the TM mws. Very reliable platform.