I won't buy into a syndicate where I'm limited to UK only.
I wouldn't buy into any syndicate where there is a doubt over getting on with the others. It soon becomes too much hassle.
the aircraft's insurance may have some caveat that would mean you were not insured.
I'd cover this by making a full disclosure of the intended use, with Art 26 references etc, to the insurer, and request a written acknowledgement.