Just like a Cactus RF60 ..... the advantage the Cactus has for now is that you can remote control your power from the on-camera transmitter, and the Flash Head Zoom as well. Without the accessory radio system to go with this flash it appears that flash power will need to be controlled manually from the flash unit itself.
Now, I'm a proponent of automatic HSS, absolutely. As I've written many times here, the advantageous in workflow simplicity are significant IMO, particularly when working in dynamic conditions such as changing ambient light (ie your sun goes in and out behind clouds), you change the flash to subject distances, or you try out different diffusers. Every one of these adjustments requires a matching shutter speed adjustment with Manual HSS, in addition to every adjustment to Aperture or ISO. That's quite a bit of extra work ...... automatic P-TTL HSS avoids this, ands that's worth quite a lot I feel. But Pentax flashes are far more expensive!
New owners here will need to check the syncing of this flash to the control pre-flashes from their on-camera accessory flashes. The S2 mode will ignore pre-flashes, but the pre-flashes of accessory flashes are more complex in HSS mode, so this may need to be tested.
---------- Post added 21-12-16 at 17:12 ----------
Originally posted by clackers So it offers high sync without P-TTL?
I may have to buy one!
I am assuming that the on-camera accessory flash used as trigger here will not be able to operate in Wireless mode .... ie it will only be able to function in standard P-TTL HSS mode with its light output contributing to the scene. So the light balancing aspects will need to be considered, unless the flash head is just turned towards the Shanny slave and the light is wasted. Dialling down to minimum flash compensation will minimise power wastage.
So if we're comparing this to the more expensive Pentax / Metz etc options, what is missing here is the ability to operate the on-camera flash in wireless 'control' mode (ie it only works as trigger signal, not to light the scene). The Shanny will not (I assume) be able to respond or sync to on-camera flashes in their 'wireless' mode. Also of course, for HSS work, it needs to be remembered that the built-in flashes cannot act as triggers, you need an additional HSS capable accessory flash unit.