Actioncam Rebel Pro owner here. Great modular system. My only complaint is that my Rebel Pro arm has no adjustment screws in the Vest-Arm Connector. Since their backmount vest has two sets of adjustments (fore-aft and side-to-side), it's not a problem. It only becomes a problem if you want to upgrade to a front mount vest, that only has fore-aft adjustments in the socket block.
Just my two cents. Apart from that glitch, it's a great system. Smooth ride on the arm. High load capacity. Very upgradable and customizable sled (my new Quattro Monitor Arm is actually on it's way in the mail right now!)