If your next question is going to be difference....
The throw is shorter. B&M shortens the throw the most (it's in low 30's%, kartboy is high 20's%, correct me if I'm wrong, Tom)
They are similar products, and all are reliable and well made. There have been no reports of faulty parts or bad fit. There is a little more resistance with the kartboy (and I assume the B&M). You also have less leverage, so that could be universal.
IMHO, go for price. I will not plug any particular brand.
But with Tom at kartboy, you get free candy!!!!