Both 'Little John' and 'Matthew Flinders' are from Callistemon viminalis so they are quite hardy. Dwarf habit makes them easy for bonsai but I find you need to do more thinning out than trimming because growth tends to be short but with very short internodes they produce lots of shoots close together.
I agree. Good material to work with.
Callistemon don't like to be root pruned down here in cold weather but up there you have a much better chance of survival. Just give them a couple of good growing seasons to get re-established before trying any further styling.
Good luck
