I think for "Testing" purposes they can log into the 4300 but it needs a direct connection (no router in the loop) That said I never give them access as I've always bridged my modems and let the router handle the access.
Since all is working fine on your end I would leave it be.
Personally I have no preference as to whether customers use Bridge or PPPoE on the 4300. We can not log into those modems remotely unless IP-pass through is initiated by the customer. Some other technicians may disagree with me but I believe that it boils down to the individual user preference.