Pro38's and the supplied ematches are great for clustering. Midpower composite clustering is a bit harder though. ML-12 Magnelites work, but not more than 4 can be used without beefing up even a 12V launch system. My favorite MP cluster igniter were the Trailing Edge Technologies "Fire in the Hole" igniters, but I don't know if they are still made as the owner, Jim Turner, died a couple years back. I belive the company is still in business, but I don't know if the igniters are still made. They were great...good pyrogen and a tungsten bridgewire. Ken at Performance Hobbies showed me some tiny igniters he has called "Fireflys" They appeared ideal for those small nozzled composite motors, and for MP composite clusters. He gave them to me to use in my Ultimate to airstart some motors, but I ditched them b/c a standard 9V battery wouldn't light them...but I'm sure a 12V system would be fine. Just test first if you use them. Plus, I wasn't thinking and used a standard 9V, which, yes, sometimes work, but I'll try a 9V NiCad next time. Quickburst is also another igniter that may work...but no more than 2 or 3 at a time there as they, like Magnelites, suck up the juice. And they are a bit worse than Magnelites. 3 would be pushing it with those. I did a twin F50T cluster in my 4-29SS and used QB Twiggys. The flight was great, but padcam video showed that one F50T lit late. So that's my reccomendations...I can't think of anything else. I wouldn't reccomend Ignitermans as I've heard too many cluster problems with those. Just remember to be wary of your power on QB's and Magnelites. 3 is enough for QB's without a relay or anything of the sort, and for Magnelites 4 is the max without a relay....hey Doug- you did 7 Magnelites, right? Didn't you use a relay on that?
Hopefully he'll answer that one. Well, I hope that helped. Good luck with the cluster!