For one of our G43s I went with having the slide milled and added a Shield RMSc. Haven’t had it running long enough to determine longevity but no issues at around the 300 rd mark. I rather like the sight size for the baby Glock.
For some. As somebody who has for years owned his products, attended his training, and spoken to him personally, I can recommend his stuff based on my experience. Others want nothing to do with him, I'm not sure if they have personal experience or if they're just regurgitating internet propaganda (regardless of validity). I just like to keep an open yet critical mind and get the good stuff wherever it comes from.
As stated previously on the only place that I have found is Suarez. That is because of the plate system that they use as the slide is to narrow to use an RMR. There is a company http://ncengravers.com/ that will mill the 43x/48 for an Shield RMS, as it is a narrower sight but not nearly as robust as the RMR. I have seen and used guns with his work and it is very good.
I ended up with a 43x with RMSc. Mainly because it was available at my LGS. I really dig the form factor. Can cowitness with standard sights. I will keep durability issues in mind. It will not get used hard or carried often, only when I can’t get away with a heavier gun. We will see how it survives saltwater exposure.
I know some on the form have issues with the owner and some of his products, but the Suarez International Narrow Slide Adaptor (NSA) is actually pretty great for this. It works on the same concept at a mounting plate for a 1911 and allows you to get a lower cowitness with suppressor sights and mount the optic with more than just the dovetail.
You can buy the complete slide from them, or just buy the plate and have a gunsmith you trust mill and install it for you.