Never ever ever buy a knockoff. That is real bad idea, because they tend to leak.
HKS and the Greddy are very similar. From my understanding they will hold up to 25 psi easily. Pretty reliable if installed correctly.
For the money Tial seems to be a good choice. The fact a lot of high powered cars use them is a good sign. Anyone I know who has had a Tial BOV has never said anything negative about it.
For the record I have a Forge Motorsports BOV which is boost rated through springs like the Tial. Haven't had any issues at 20 psi.
