The belt grinder is the cleanest option. There is no stone dust from the wheel. Metal off the blade is the same.Both companies have been around forever. Magna-Matic has at least somewhat embraced the digital age and has a Youtube channel and a little social media presence. RBG still uses B&W pictures of most of their products. That's pretty lame even by late 20th century standards.
The motors MM uses are US made and industrial grade. Their RPM is also twice that of the RBG. Can't really tell too much about RBG's motors, but in one of their pictures I saw where it said it was made in Mexico.
I like belt grinders for the other things they can do.... but aren't they the least clean option? Don't the shavings just go everywhere?