I've used them in a two motor cluster and they worked great. It was two F50T's. They're reliable an relatively easy to light, however aren't designed for clusters. Using them for a cluster of more than 3 motors is iffy. I understand that Quickburst now makes igniters especially for clustering. Send David Bachelder and e-mail...he's a nice fella.
Well, my TARC team, dyna_soar, and I successfully ignited two G64's with these ignitors! They ignited almost immediately. I can't see myself, or the others, going to any other ignitor for clusters. At $1, you can't go wrong!
Good job with the igniters, Mr. Quickburst, I'm sure you browse through this forum.
I'll confirm what Quickburst said. Tried to light 4 AT E15's using Twiggy's with a 12 V system and had none fire. Tried again with some Frogs, igniters that he used to make for airstarts, and had all fire.