Since Pentax doesn't make a dedicated grip for the DS series, aftermarket is the only way to go. Two options are the Dicain you listed and another is Ownuser. IMO The Dicain looks more OEM and looks like it belongs on the camera. I have one and it feels great in the hands. I haven't had any problems with quality in the 9+ months I've had/used it. The vertical shutter release is great for portrait style shots and it comes with a remote tucked away in the grip that's useful as well. It does not however accept extra batteries so don't think of it as a battery grip like some people assume. You can check out more photos on their
site. Everything's in Korean, but you can look at the photos. You can also
contact them in English as well if you have questions or want to order.
The
Ownuser is a lot bulkier - however it does accept 8 extra AA batteries for backup. But IMO, that's overkill and having two sets of rechargeables is more than enough for a shoot. I can't comment on feel and quality since I've never used it.
The Dicain seems easier to get a hold of; there should be a few users who have it. I haven't seen anyone with the Ownuser grip.