Staged Composites is mostly what I've flown the past few years:
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I also use the eggtimer products. A GPS Mini in the nose cone of the sustainer. Quantums and Protons for staging. Sometimes a Quark in the booster for deployment redundancy.
The Quantum is smaller. I've squeezed one in an Estes 5560 transition for my Nike Apache - but it wasn't easy. I've wedged a Proton into a Wildchild (about BT60) - but 2" and bigger is -so- much easier.
As Waltr mentions, the Quantum is the practical minimum in capabilities. In airstart mode, the second channel -has- to be the drogue. You could always add a Quark riding along for full dual deploy. The Quantum is purely baro driven, and while the combination of a decent sim, and the altitude and velocity checks at staging time will keep you out of most trouble, it has its limits. Mostly erring on the no-staging side. Your avbay needs to be properly vented - and in such a way that doesn't add error - protruding or shadowed vents can be a problem. It's also slower to respond - so it needs higher staging altitude and coast times to let disturbances settle down. Not huge - but since I fly at Bong (with trees and swamps) I try to fly as -low- as I safely can, and tenths of a second add up fast. Motor burnout and separation cause big baro-altitude swings in my avbays.
I really like the Proton with 6 channels. I like using a tiny separation charge - I just pack the little red cap of an ematch with black powder. I really like the time-after burnout option that the Proton had, rather than the time-after launch detect of the Quantum. The accelerometer based launch detection is quicker, too - 75' isn't hard - or dangerous from the false positive sense. And even adding dual deploy, there are still 2 channels left - perhaps separation and ignition of a middle stage. That's a lot of wiring chases in the top stage, though.
With either, you can add a separate tiltmeter if you think the 'deviation from planned Alt/V' limits aren't enough.
Rocket Electronics - home of the RockeTiltometer (rocket-electronics.com)
I'm working my way towards 3 stages. A Black Brant, like yourself, and a Talos Terrier Recruit. But I think my first might be a Nike Nike Cajun. Or maybe I'll cheat and do a mythical Nike Nike Apache.