The mint reads BN but I don't know if that is significant for the Islamic issue or if it is just what the coin they copied was. I don't make sense of the date. As far as real/fake goes, I am not comfortable with these to the point I buy coins from questionable sources. I see nothing that makes me think it is bad but I don't know enough to say one way or the other.
As I said before, I'm not an expert in either Sasanian or Arab-Sasanian, but I own a few and have read a bit on the series, so I'll give an opinion. I don't see anything obviously wrong about any of the coins @arashpour posted. The porosity of the Arab-Sasanian and the other may be due to partial crystallization of the silver. This sometimes happens to ancient silver coins, which results in loss of material and thus light weight, and such coins are less valuable than undamaged examples of the same type. I've never heard of these being copied in plastic, I can't say it's impossible but I would expect any forger to at least use some sort of real metal. Album lists BN as a rare mint for these early anonymous Arab-Sasanian types (a few dozen different mintmarks are known), as far as I know mint marks on these are the actual mint but I could be wrong. I think the script on your Hormizd coin is correct, considering the fact that Pahlavi script is terrible and often hard to read even on perfectly preserved specimens. Also, I would second Doug's suggestion to only buy coins from sources whose honesty and expertise you trust. Actually, that's good advice for anyone.