The '70-'79 650 regulator is the power controlling type. It's the '80-'83 650 regulator that controls the ground, and that's what that eBay reg/rec looks to be. The bikes-it-fits list has errors in it. It says it fits all models of the XS750 triple but that just can't be true. I know for a fact that the early models, the '76 and '77, used the same power switching regulator as the '70-'79 650 did. But the '78 XS750 switched to a ground controlling regulator like the '80-'83 650 uses. All the other bikes listed, the XS850 and XS1100, also use the ground switching type regulator. Even if it was the correct type, being such a cheap Chinese product, it probably wouldn't have lasted for very long anyway.
Honestly, in my opinion, the best reg and rec set-up for these stock charging systems is to use an automotive regulator and a rectifier from the electronics world. The VR115 is a power switching regulator suited for use on the '70-'79 650 systems, and is what most of us use. It has been used on cars since the '70s and is a proven, reliable unit. They can be had for between $10 and $30. A good quality 3 phase rectifier from the electronics world can be had for about $10. It's just plain crazy (and STUPID) to be spending $100+ on those motorcycle specific units.