The latest driver on SeriTek's website is 5.1.3
https://www.firmtek.com/download/
All the firmware drivers for this card are buggy in some way. If you look on the Sonnetech website, the FAQ for the rebadged SeriTek card it sold suggesting downgrading the firmware to an earlier revision if you had issues.
Have a look around the forums for the Si3112 card. You will find plenty of threads, including where the firmware writer for the original card had a go at writing a new firmware before he disappeared again. There are also a couple of threads on MacOS9lives forum where he popped up as well. There should be a couple of threads where a couple of revisions of the firmware are knocking around.
The HK sellers are just using info gleaned from this and other forums to make a quick profit from the unsuspecting. They don't have much knowledge about what they are doing. To be honest, this card is only interesting if you want SATA support under MacOS7.6-9.x. If it is just OSX, there are other, cheaper options.