I doubt if they are as well maintained in linux distros as the GNU tool set, particularly in terms of having recent fixes backported into the versions carried in enterprise distros.
They are updated pretty much every month.
My basic requirement with what I'm doing is to use standard tools and formats so that archives I write today can be readable in 10 years.
I've never had any doubts that current GNU tar would extract archives made with it 10+ years ago - in fact I'm fairly sure I've done that. Or that I'd be able to obtain a copy of it in the future.
GNU tar .. has its own bugs. Is it really standards compliant?
Is the use of Schily tools going to be contrary to my basic requirement? Is that considered a risk for future readability?
It shouldn't matter if you don't use either of the version's extensions, and for archiving you probably don't need them. For example, star and GNUtar use very different concepts for incremental backups - star is sort of like dump and must work on filesystem boundaries where GNUtar's --listed incremental needs a file to hold state but will work on arbitrary directories and can span mount points.
same sort of deal with star .. but you should go ask the author.
dc