For production might not worth, but for students/makers/hobbyists who do not care about the provenience of the .lic files, and also have the time to reverse engineer the PCB, $75 is a bargain.
The only thing that might be a showstopper is when the FPGA is a pre-engineering sample. These are usually distributed in very small number to big OEM contractors only, so the OEM can develop their own products based on a not yet launched FPGA. Such samples have "incomplete" silicon, good to load/test HDL designs, but they are not fully working, for example they don't have the IO pins connected, or things like that.
Since the ebay lists many boards, those are most probably fully working FPGAs.