In my opinion the biggest single draw back to a TLR is lack of DOF preview. I have little regard for the DOF scales on the Mamiya. The Rollei cameras that have DOF scales are really slick.
The Mamiya 105mm lens has DOF preview for use on their TLR cameras, it doesn't get a lot of press because the 80mm is a better lens. For landscape work, put the 55mm on (aperture f22), focus on something close and fire away. Everything is in focus, and mighty sharp too.