I moved this post out of the compliance thread, because this question has nothing to do with "handgun compliance". Most handguns in MA are legal unless they are assault weapons, which anything that's a derringer won't qualify as, usually, because
there is no magazine involved. On its front derringers are "possession legal" in MA.... it's just that they cannot be transferred by a dealer unless they are papered exempt.
Now, that aside, this is a tricky question. I know Federal law, and probably MA law, makes it a crime to own a gun that has a defaced serial number, but it doesn't address what to do about guns that have no serial number. At one point in history many guns have no serial number, even some "modern" rifles and shotguns that were made a long time ago... and those are legal to own... so no reason why a pistol wouldn't fit this description.
Another thing to watch out for is if the gun is rifled or not. IIRC smoothbore pistols that take centerfire cartridges may be
considered NFA devices by federal law... but that's a whole other ball of wax. The only reason I mention it is some
homebuilt contraptions often use things like smoothbore barrels, etc. I'm guessing this device takes centerfire cartridges?
-Mike