I have both the referenced HDHR Dual as well as the cable-card-ready HDHR Prime. Both operate the same. The dual has two tuners while the prime has three tuners. If you aren't subscribing to any cable programming the prime currently is not of interest to you (see below).
The HDHR units are network-based tuners. You need something that can control the tuners (select tuner and change channel) and something that can receive the stream, decode, and display. For now this means you need something running on a PC or Mac such as eyeTV to control the HDHR, even if you are only streaming to an iPad.
However, there is a beta program running (Project: Connect) with the prime to add DLNA support directly to the HDHR. This means you would be able to control and view from the HDHR on your iPad without something like eyeTV running on a Mac (or PC). An app on the iPad would be able to do everything. It only appears that this will be for the Prime (and later), however, so you may never see this with the original Dual you referenced.
SiliconDust manufactures the HDHR devices and is at »www.silicondust.com/
Their forums are decently active and may be a better place to ask this question: »www.silicondust.com/forum2/
There are a few forums that may be of interest.