Is this your first rotary cutter purchase? I think you'll do better with the more common brands. Not to dis Martha, but she's not known for her quilting tools.
Rotary cutters are kind of personal. Some have features quilters love and other quilters hate. If you have never used a rotary cutter, buy one within your budget and practice. You'll get used to it and it will probably be the only cutter you'll ever want or need. Change your blades often. It's not worth the arm pain or skipped threads to deal with a crappy blade. The blades are not cheap, but having a sharp one makes all the difference.
I experience cutting fatigue often. My hand and elbow get it if I cut too much. I'm in considerable pain if I continue cutting. Sometimes there is swelling or tenderness. So far, the only thing that helps is to let everything rest a couple of days. I can usually get back to chopping, but I make sure I have a sharp blade and I'm not putting pressure on my joints.
Good luck fining your cutter. Be safe with it.