Same kit, different box.
Instructions in the RoG version are probably their multi-language versions. The Revell USA instructions are all English with French warnings
The molds were designed by Revell USA using the Silversides at Manitowoc Wisconsin as the subject. Manitowoc is just up the road from Northbrook Illinois, Revell USA's home. Revell USA & RoG did cooperate in the molding & production
SMO probably has to cover import duties for the kits coming in from Europe.
Then again, it may be a case of 'it costs more so it must be better, right?'