While lable say ok for primary there are many that argue SYN do not belong there because of the wet clutch. Thinking is it is not good for the clutch long term.
I have used Redline SYN primary lube in the past, and had no clutch issue, but that is a product designed for the primary and not engines.
I know several riders that use SYN engine oil in the primary, none have had any issue yet.
The Redline was ok in primary when I used it and would have no problem with using it again myself.
Spectro is easier for me to get HD dealer carriers it and is low cost.