It has auto mode - It's called P-TTL.
Just put the unit in P-TTL mode and that's all there is to it. You can put the camera in all green mode, fire off at will. It works just like the pop-up flash would but is obviously far more powerful and much more useful. (if you don't need the most powerful setup, you can get a little less powerful unit for $169 and $200 - look at promasterflash.com or the promaster flash website might be best)
When you use the camera in a mode other than green like M or TV, etc you control the flash exactly the same as you would the pop-up flash, you can compensate for flash exposure by dialing it down -2.0 or +1.0 ... trailing curtain, leading curtain, etc..
But yes, it is a fully automatic flash that needs no other input from the user other than to attach it to the camera and make sure it's in TTL mode. It fires off a pre-flash just like the pop-up does, measures the scene from the pre-flash, then fires off the main flash for the shot with an adjusted output level to give proper exposure.
FYI: So far, so good.. I've been using it to light up birds at 50-100ft with no problems whatsoever. And if a bird is really far away, like say 150 to 200 ft or so, I've been switching to manual mode (press one button) and getting enough flash to get a catch light and put a twinkle in the eye of the little bugger. So, yes. I've been quite happy so far. And something the literature of some flashes is confusing on, when you use the the flash in P-TTL mode it has a reduced range, for this unit it's between 1-99ft, in non-P-TTL mode it's good to 138ft - All flash units are like this but some are like, 1-24ft only in P-TTL mode. In this respect this flash is good. I'm looking forward to using this unit with a better beamer for some long-distance and increased DOF shots as the unit is capable of a very wide area of coverage which when used in conjunction with a better beamer translates into very focused beam at long distances.
Another thing, I honestly thought that HSS was something I would miss. Then I thought back to 15 -20 years ago when I shot as much as I do today but in film with a flash that was no faster than 1/125 or so.. I thought, how did I stop action then? Well, simple really.. I just used a slower shutter of about 1/60th and relied on the flash to stop the action as the flash is faster than any shutter at 1/30,000 of a second
EDIT: I just realized that you meant Auto mode as in, Auto and not relying on the camera for exposure information.. That's some pretty old-school stuff. My Vivitar 283 has that. Try this
Promaster FT1700 Bounce Thyristor Flash Brand new $39 and has Auto Thyristor by Promaster FT1700 (looks like my Viv 283 lol) P-TTL supercedes auto-thyristor, sort of.
Read this thread in it's entirety
Wedding and social event photography Forum: Opinions about Promaster 7500DX Flash - photo.net
Oh and, god forbid you change from Pentax, you can just buy the module for whichever inferior brand you go with and still use the Promaster 5xxx series flash with the n3ew system