You need to periodically take it apart to clean and re-grease the bushings or else it'll eventually seize... not something you have to do with the standard twin shocks.

If you're thinking aesthetics also take a look at the frames that the Pro-link bikes have and compare them to the standard CX500 or CX650 Custom - the Pro-Link bikes have a flat-ish section of frame running down either side which is a different look to either of the other two (single spine for original CX, tubular section for 650 Custom). You may like it more or less...

 

I definitely like the clean single back bone, but want a better performing suspension as well...

 

The merits of the suspension designs aside, the frames designed for Pro-Link are significantly better engineered. As for servicing the Pro-Link, if you do it right one and add zerk fittings and drill through the bushings to get the grease through to the bolts as well the annual service can be reduced to loosening the bolts/nuts, pumping in fresh grease until it comes out around the bolts and tightening them up again periodically - maybe 10 minutes extra every time you change the tire.

BTW: Do you realize that your CX500 is CDI and all of the 650s are TI, which means extensive rewiring to put a 650 engine into a CX500. If I was doing it I would use the entire electrical system from the 650. If you don't do that you will need to modify wiring to suit the TI units, re-wire for the ignition keyswitch (this is NOT plug & play) and figure out where to connect the fan.

 

Sounds like with some prep it may be easier to maintain... I'll look into who's done one of those zerk fittings. I hope someone was nice enough to show how to do it.

I was planning on swapping what I needed from the 650 and do an M Unit for the rest.

 

It really depends on what visual style you want to end up with. For my personal build I had a pretty clear idea what my end product would be and for me a GL650 made the most sense as a base for the project. No need to use 2 bikes to make 1. My buddy was building a CX at the same time and really wanted a mono shock. His started as someone else's unfinished project and it already had a poorly done monoshock conversion. We had to redo everything.
Here are some words of experience; There are dozens of really cool looking monoshocked CXs out there. You might also notice that it's rare that they are actually ridden. That's because many factory monoshocks don't have a very high spring rate. We tried 4 or 5 different units and even the final one he settled on is a bit soft for my liking. Please resist the urge to choose form over function. Your life may depend on it.

To answer your original question, Yes, the ProLink system works fine. I've had mine on-road and off-road and it works well with no problems. Rather than muddy your thread, our build thread is linked in my sig if you want pics and details.

 

I did see your build!
Function for sure. I'm thinking that adding a linkage system is the best way to go and the prolink off a GL would be the easiest way to make it work. rather than building a linkage rear suspension and modding a CX 500 swingarm sounds like more work than what needs to be done.