Wilwood master cylinder

EX 500 mc works as well. It has a 14mm bore compared to the 17mm bore of the ZRX. Actually my memory is failing me but the ex500 mc bore is small enough to make a noticeable difference in brake lever pull over the ZRX.
There is no difference externally between the two.

I installed and bled the ZRX1200 MC today. It works loads better than the Amazon one. I was also reminded today why I didn’t want to swap MCs, the dual calipers are an absolute pain to bleed correctly. Got it all figured out though and I am happy with the change. 

The ZRX owners go with the ex500 MC.

And often four piston calipers from 1990s Suzukis.

Not sure about the EX500 MC but I wanted to provide my honest opinion on the ZRX1200 after about 100 miles of use. Holy cow what a difference it has made, the brakes are more responsive, the lever adjustment is extremely helpful and better than the 14mm bore of the Amazon MC, I don’t have to pull the lever halfway to get a decent stop out of them. If anyone is ever considering picking one up I would definitely recommend it! 

I just looked at the Amazon listing for my old MC and it has a 14 mm bore, it I definitely prefer the increased braking ability of the 17mm bore from the ZRX1200 Master cylinder.