@ Compucat : I'm afraid I can't explain why that's happening with you. The library appears to work fine with the S25FL127S I have. I'll try out a few other chips this weekend and let you know if I face any issues.
@ TrekRider: I'm afraid the library does not officially support the BluePill. I have had a lot of trouble getting the USB bootloader working on my boards and gave up just before Christmas. However, I'm still keen on supporting the board, so, could you do me a favour and raise an issue on the Github page [here]? I'll get going started again on getting the Blue pill supported. 
@ kucukkose: Thanks for raising an issue on Github about this. Could you please refer to my comments there and provide a little more information on what exactly the problem seems to be?
@ Gosh: What do you mean by simple sketch to demonstrate read/write operations? Are you looking for code that works with the SPIFlash library or SPI level code?