The Royal engines are indeed knock-offs of the older OS FS series. They were made offshore, and the later ones were made by the LEO engine company of Taiwan. You can still get the LEO engines under their own name, and I think they also make engines sold under the Thunder Tiger and MECOA names.

I have a Royal 46, which I used briefly in my LT-40 trainer. It was a bit finicky and I think the throttle/carb is not quite as well built as it might be because throttle response was sloppy sometimes. On the other hand, I only flew it for a while before switching to another engine because the unreliability was holding up my training.

I have no reason to think that the engine could not be made more reliable with very careful adjustment of the low-end needle and general attention to the carb.