Disclaimer: I don't have that particular flash unit. So below are my feelings, I have nothing to back up:
1. Sunpak does not have dedicated module for Pentax DSLRs that supports p-TTL.
2. If the dedicated module for Pentax DSLR did exist, you'd have to buy it extra. That plus the cost of $270 for the flash would push the price nearer to that of the Pentax ringflash AF160FC (about $450).
3. Without p-TTL support, this flash is essentially the same as the Sunpak DX-8R, which I have a copy of. If you are patient and lucky, you can find a used copy for much less than $270.
This is an example.