The 285HV is not P-TTL but it is a huge *ss flash!
You have to use it manually reading off the calculations on the guide on the flashe's side.
I don't know anything about the Metz but I am happy with the Tumax brand flashes such as Bower SFD926P, Rokinon, Vivitar DF383, Digital Concepts..all are power zoom and just have different re-brands but all are made by Tumax.
These are P-TTL with optical slave built-in too!
They also have a bulit-in pull-out diffuser and card bouncer.
All it lacks is the wireless capability of the OEM Pentax flashes.
These brands that I mentioned also offer models that have a manual zoom head instead of the power zoom feature or a much lower model with just a bounce (minus the swivel) feature.
With the power zoom feature with bounce and swivel they would cost around $90+ to $120+.
With the manual zoom feature with bounce and swivel they would cost only $80+.
For just the bounce featured models, they are about $50 (mostly Rokinons).
I use this more (Bower SFD926P) than the Vivitar 285HV.
P-TTL is the way to go!