I have 2 of the HDHomeRun DUEL units. I think they are great. I've never had an issue with them.
To me there are 2 main benefits to the HDHomeRUN units:
1) You can run multiple units on the network. As stated I have 2 now, but it could just as well be 4 and each unit has 2 tuners. So today I can record up to 4 shows, or if I had 4 units, I could record 8 shows. I'm not sure if JRiver has a limit or not.
2) Location. I have my antenna in the attic and the two units mounted to a laptop cooler in the attic as well. (Attics get hot so I figured why not.) Anyway, RJ-6 cable as 6 dB of loss per 100 feet (plus at least .5 db per connector). I needed about 40 feet of a 50 foot run to get from the attic to my network switch (50 feet would be 4dB of loss; 3+1). Therefore, by moving the tuners to the attic next to the antenna I gained 3dB of signal strength. For most channels I was fine before, but now I don't get any pixelation on any channel, so it was a good move.
Card based systems can't compete with benefit #1, though a USB setup could.
USB based systems can't compete with benefit #2.
Future benefit - Silicon Dust is adding DLNA support to the HDHomeRun line so in the next few months any DLNA client will be able to access the tuner and watch content.
Sub benefit - I rent out 2 rooms of my house, by using network based tuners, they can run their own media player and watch TV in their room on their laptops with no issue. Also, with 4 tuners I have not run into any issue of us fighting for a tuner either so big plus there as well. But if we do, I just buy another unit and bam, 2 more tuners, problem gone.