While I have never owned one, I have had some experience with RE. Mostly working on them. The main problem with them is the terrible quality. This applies to both materials and workmanship. The metallurgy is awful. They are made out of what is commonly known as "pot metal" It is very soft. Fasteners are easily broken and stripped. The internal engine parts are no exception, the metal is so soft that pistons can melt under normal operating conditions. The other problem is manufacturing tolerances. They are horrible compared to modern Japanese motorcycles. New ones come with bearing clearances and piston/cylinder clearances that are so far off it's a wonder that they even run. One of the main reasons these engines fail is that they tend to run hot, and when they get hot, the clearances get even worse, causing something to break or seize. I have replaced 3 kickstarters on earlier models, because the gears stripped. I find this simply unacceptable for a motorcycle that costs this much. My Yamaha XT225 will run all day at full throttle with no obvious ill effects. In fact it has done so for over 20,000 miles. It does not burn oil, and compression is still within spec for a new engine. Yes, it has been over maintained, but if I had a RE it would be too. But it wouldn't help much.
The real shame here is that it doesn't have to be that way. It would be easy to design and build a motorcycle that looked exactly like the RE, but with modern materials and craftsmanship, that would be every bit as reliable as any Japanese bike. Look at the Honda XR650, Suzuki DR650 and S40, all 650cc single cylinder air cooled engines with great reliability. Such an engine could be designed to look almost exactly like the RE engine. You could have your vintage bike, but with modern reliability. You wouldn't even need the FI, none of the above mentioned Japanese bikes have it. I wish Suzuki would build a TU250 styled bike with the S40/Savage engine, and a centerstand. I would buy it. I would also buy a reliable Royal Enfield. But I'm afraid that as long as it is made in India, such a thing will never exist. I would love to see what the Japanese could do with the RE without changing it's appearance.
2002 Vulcan 750, 2001 XT225
2008 Vino 125, 2009 Genuine Stella
2012 Zuma 125, 1980 Puch Newport moped