Here are a few random thoughts, although I am by no means an expert, especially with the likes of others on this board.
The Knight Rolling Block would be a great gun if you had no intention of shooting BH209 in it, due to ignition problems. If you plan on shooting BH209, I would look towards a TC Omega or Triumph. The Knight Disc Extreme should also work well with BH209 depending on the breach plug. There are other Knights that would but I'm less familiar with them.
FYI BH209 is a new non corrosive BP substitue recently introduced. I think it would be a great place to start. It requires no swabbing between shots or cleaning before putting away at the end of the day after firing.
Best advice would be to go to a store that carries ML's and check them out. If it doesn't feel/look good in your hands you probably won't be happy with it.