RE: TC Thunderhawk 54 cal.
The only experience I have with one is a person I know many years ago, bought/won one by accident. I kid you not. He put a dollar or two into a raffle pool and ended up winning one.
When he brought it over to show me the rifle, hedid not even know what it was or how to shoot it. So of course we had to play with it. We found out real fast that with 90 grains of Pyrodex and a buffalo bullet conical it was an extremely accurate rifle. I remember after we shot it I offered to buy it from him but he decided he would use it in the shotgun only area where muzzleloaders are allowed. He mounted a scope on the rifle, and he still shoots his deer with it each year.
The 1-38 twist they had were real conical shooters. I am sure there is a sabot out there that they would shoot as well. The real problem I see with people that own them and want to sell them is the price they are asking for them. For what they are asking, people are finding Omega's even cheaper. In that case,I would take the Omega.
Although if you can get the rifle reasonable and in NIB condition I am sure it would give you many years of hunting once you find the right projectile.