For US/CA/IE/UK/NL the outstations are fully 'online' (though this may not be the case if the destination is a Regional only location) and you get the full experience and the standard boarding card, on EI stock which will show status and priority boarding etc

Elsewhere the check in is done on whatever system the local airport you use. It in no way impacts your luggage or status entitlements but it won't show anything.

As far as I know you don't get priority boarding with Avios tickets, its just a quirk as to how the system handles them