While I haven't seen e-rockets MMX offerings. I can say I have several 2-stage MMX rockets flying on the NE to MMX-II motors. I can attest to the fact the avg. .82sec delay between NE burnout and upper stage ignition can be heart stopping but I've yet to have even the heaviest Micro Two-Stager do anything other then slow down a bit.
One of the best micro-maxx designed 2-stager is Fliskits "Doubles" not only is it two staged but uses T3 (.375") tubing making it the perfect frontal area to thrust combination. It stages at speed making for some out of sight flights.
I have some minimum diameter T2+ two-stage downscales Hercules 2-stage & Warp-II that I don't fly very much unless I have a lot of other people around as they both are nearly out of sight at staging making recovery of both parts very difficult. So far the Hercules has flown staged only 3 times. while the yellow painted Warp-II has flown a total of 8 times including at one Night Launch (almost a first stage mistake). T3, T4 and ever BT-5 (T-5) Bodies seem to be the best choice for multi-stage micro rockets.
One of the best micro-maxx designed 2-stager is Fliskits "Doubles" not only is it two staged but uses T3 (.375") tubing making it the perfect frontal area to thrust combination. It stages at speed making for some out of sight flights.
I have some minimum diameter T2+ two-stage downscales Hercules 2-stage & Warp-II that I don't fly very much unless I have a lot of other people around as they both are nearly out of sight at staging making recovery of both parts very difficult. So far the Hercules has flown staged only 3 times. while the yellow painted Warp-II has flown a total of 8 times including at one Night Launch (almost a first stage mistake). T3, T4 and ever BT-5 (T-5) Bodies seem to be the best choice for multi-stage micro rockets.