I've been using an older model GWiz for composite staging and haven't had a sustainer fail to light yet.
My first outing was with an Aerobee Hi and it staged very nicely on its first flight.
The subsequent flights were all confidence builders and very satisfying.
I have a large 1/3 scale scratch built Wac corporal that is designed around Loki 38mm hardware...the sustainer has flown several times but I got a little nervous about flying it two stage after seeing an interstage fail on a large two stage project.
Of course the interstage of the Wac has a scale like framework...a tube coupler style interstage like the Quantum Leap or Nike Terrier maybe stonger and easier to align.
If you design it... consider the fit of the interstage area.
I'd love to see a "Basics of two stage composite motor rocketry design" resurected here...
IMHO - I think it wise to progress carefully with composite staging as the failure modes can have a nasty "downside" ..especially when you get into large motors. There are a couple of bad ones in the Rockets DVD "cool flights and really cool flights".
Seeing what was left after an M two stager turned around midflight and then fired the sustainer back into the launching area was sobering to say the least..............
I'm looking into this adept device.....for my three stage project. I like the failsafe concept for the third stage...
Adept ES236LH Dual Sequential Stager
https://www.adeptrocketry.com/ES236.htm