My local store, Poco Military Surplus, has since discontinued the sale of Typhoons in favour of the Derya models: The Typhoons suffered from badly polished internals over that of the more refined, and slightly more expensive, Derya shotgun.
That said, Although one of the chaps on this board suffered a lemon, it was the store's experience that the Typhoon was returned for fixing at a rate of 100% - with the exception belonging to those capable of diagnosing and smoothing their own internals.
Now, the only Derya "problems" seem to be from noobs unaware as to how to operate their gas settings.Derya +1 [Even though I own a FD 12 'cause bullpups are cooler].
Cheers!
~ Tom