SunXCD has only been available for a few months I think, and not many folks are going to have much experience with it. It certainly looks great. Where did you even find the 3 arm chainring type? UK vendor? The cranks don't come in 175 or I probably would have got a set.

The other competing retro group is the Gran Compe ENE, which is pretty nice too. Both groups use microshift sourced derailleurs.

FWIW the Microshift Centos is a notch up from the R10, and has a little fancier jockey cage. It appears to be pretty much the same derailleur as the SunXCD. It only comes in a short cage AFAIK, so if you want the GT version, got to pony up for Sun XCD. Also I think the silver model has just been superseded by an ugly new white painted version, but the R10 is pretty close and still silver.