Not to start a pissing contest, but I am a Rotax Certified Tech (for airplane engines) and almost all of the Rotax 582 two-stroke engines used on ultralight and experimental aircraft I work on are running oil injection. I have worked on over 200 aircraft with various Rotax two-stroke engines. The 503/447 are almost always premix (for the reasons you stated), but the 582 is almost never premixed. Also, I have installed several oil injection systems on premix engines (503's) with no failures.
I do know of two definite oil injection failures: root cause was stuff in the oil tank, one was a sliver of foil from the oil bottle, the other a small piece of plastic. Putting a filter in the oild line would address this issue.
I run oil injection on my RG-250, RZ-350, and three snow mobiles without issue. I use these machines all the time. All of my snow mobiles have at least 4000 miles on them each. My first RZ-350 had 70,000 miles on it when it was stolen, oil injected the whole time.
I read the Beta system will have an indicator if not working correct, which is something that other oil injection systems do not do. The best we can see there is low oil.
I am buying a CT, and not worried about the injection. It is very convenient, and is better for the engine over the long run.