Web site: 5050DXR Digital Flash Module
Key Features: AF assist beam.
Reasons to Buy: Works on all the 5000DX series flashes.
Notable Drawbacks: Bought separately. A little clunky.
This isn't a flash, hopefully obviously. It's the Pentax-compatibility module used with the 5750DX or 5250DX. If you get one of those flashes, you'll need this. This may be an appealing option for people with multiple camera systems: you could share the same flash between Pentax and Canon, Nikon, Sony, or Olympus.
More about the Promaster 5050DXR can be found on these pages:
Including an Amazon link on this page is the easiest way to display the current prices, without having to keep track of it manually or write a more-complicated tracking script. And as a bonus, there's a picture of the flash. Obviously, the ad is also an affiliate link. As with all advertising on this site, I hope it's not too obnoxious.