Let’s take a minute to crack this case and answer all your questions!
WTMG's Heidi Hawes: "While I did enjoy my time with both of the Famicom Detective Club games, I will say that The Girl Who Stands Behind is definitely the better of the two. The darker storyline, complex characters, and addition of a few speculation mechanics made for a more polished and captivating experience. I would still recommend picking both of them up as there is the option of purchasing them bundled together versus separately. However, I would advise to play them in the order they were originally released, with playing The Missing Heir first and The Girl Who Stands Behind second. Although, if you can only afford one of them, then go for Famicom Detective Club: The Girl Who Stands Behind."
If you’re going to play just one of The Famicom Detective Club titles, The Girl Who Stands Behind is the one to play.
Famicom Detective Club: The Girl Who Stands Behind offers a much more enjoyable experience than The Missing Heir. Here's GotGame's review.
None they are a rip-off.