I haven't heard of anyone using ametalene, but perhaps someone else has.
I have a very hard time getting MAPP gas and instead have been using MPS (sorry don't know what it stands for) that is also sold as a braising gas. I know you can use propolyne which also burns hot.
I switched from the MPS canisters to a 5lb propane tank. I have all kinds of issues with the first tank of propane through, but after that it's been pretty good. I find it hotter than the MPS canisters and can run for hours without the problem of having to warm the tank.
I have had some soot when encasing, but I think that is mainly from working to close to the torch, as I know many people seem to be able to clear encase cleanly.
Here's a link to a thread dedicated to hotheads.
It's very long, but there is a wealth of info in it.