I just do not know about the S model. What I read is the same as you however. I have seen a couple at our field and they are fine running engines. I just have not had any real time with one.
So I can't say either way.

As for breaking in.
ST says you run them WOT 4 cycling for about 5 minutes,lean a tiny bit,wait, lean a bit,wait, etc. Continue this for 30 minutes or so. It is detailed in their manual.

This will break it in good enough to start using the engine.

It will not reach peak performance until a gallon or two of fuel is used. Keep it rich, more then ideal, but not slobbery, it needs to heat up for proper breaking in. To rich and the temps are not right.

Keep it that way for a gallon or so.

You will then be able to get some good peak tuning. The ring and sleeve need to wear some, it takes a while for that fit to be perfect.