My answer would require the definition of "Investment." First, my Caveat: I don't look at, Buy or grab any gun as a collector, or to wait for it to appreciate and become "more" valuable. I look at guns as working tools or working toys. Either way, "working" applies. I just don't see "investing" in guns to be a valid alternative to Robbing Banks.
Too the guns themselves. Miroku make fine guns. Their machine work is superb. Well maintained, it would be reasonable to expect them to perform thru regular use and out last you. By a lot. My personal opinion, those who cut up really nice double guns for CAS are really missing the boat. There are a plethora of inexpensive Double Guns nobody will miss.