Yeah, Clsuters and Air-starts were great. Used T-lite with Flashbulbs for clusters for many years. Recent years, have used Quest Q2G2 ignitors for BP clusters, but those have become hard to get..
One of my favorite air-starts was with an R/C Rocket Glider to fly in "G Rocket Glide" At NARAM-34. It took off on an F10 but was a bit heavy for an F10 and also it needed more Total Impulse to qualify as a G powered model. So I had a D12 in a second pod. But I did not want to risk a cluster, in case only one motor lit. So, Thermalite in the D12, ignited by the exhaust of the F10. Took off a bit slow than about 1-2 seconds later the D12 lit and it was like going to "Afterburner" while the D12 burned. Then the D12 burned out and the F10 continued for the rest of its 8 second burn, at a much faster velocity than before. Flight two, took it a step further, with a second F10. It lit about 4 seconds into the first F10 burn, but the model got so FAST with the combined thrust until the first F10 burned out, that the model almost went out of control, pitching nose down slowly and full up elevator could not stop it. Worked out though, first F10 burned out before it got too far off-vertical and I got it under control for the rest of the 2nd F10 burn.
And that was the fun, simplicity, but also risk of Thermalite for an air-start like that. I could not time the ignition of the second F10 as precisely as I needed it to (wanted it to ignite 6-7 seconds after the first F10 lit, for only a 1 to 2 second thrust overlap). But that was the only time I really needed an air-start by Thermalite to be that accurately timed.
Nearly all of us (without old stock, or in Canada) have learned to fly without Thermalite. But, still, there's still times when it would be SO NICE to use , instead.