The customer is king, and it doesn't matter if the weapons they purchase are suitable or not; that's their freedom.
As the saying goes, "Money can't buy happiness." On this matter, Shinra's military industries are quite clear-headed, never forcing customers to buy products they don't like.
There are no technology embargoes or export restrictions. It's the 19th century, and even if you gave away all the weapon blueprints, very few countries could replicate them.
Reverse-engineering from weaponry is even more unlikely. Perhaps only the British could manage it, but even if other countries deciphered the technology, they wouldn't be able to mass-produce it anytime soon.
So the question arises, what could the British do with a bunch of new army equipment?
Surely they're not planning to compete with Shinra for the arms market?
Keep in mind, we are in a great era of weapons renewal. Today's advanced technology could be obsolete tomorrow.