The original PSX4Droid was developed by ZodTTD and was yanked from Google's Market earlier this year, along with many emulators and applications by fellow developer Yong Zhang.
However, this version of PSX4Droid appears to be developed by somebody else entirely, listed as SnootyKing. Currently, PSX4Droid is the only app attributed to this developer. According to DroidGamers, though, SnootyKing is a member of the emulation community and is looking to continue the project.
Sadly, the app is still suffering from technical bugs, such as redirecting users to the Android Market. Most user reviews are also negative. Considering PSX4Droid costs over £3, we recommend that you wait for further updates and improvements before downloading it.