I've had my Primus for 2 or 3 years now and on the whole I am very pleased with it. Playback (the most important concern) is flawless. I tend to watch MKV and AVI mostly.
Where it is lacking most is the interface. All you see is the 8.3 file/folder name. There's no icon, no last watched date or watched indicator (We've been watching Frazier and Cheers with hundreds of episodes. Remembering where you are is a pain) etc.
You can't copy files from USB to HDD or organize on the unit, so for every change/added movie you need to unplug everything and take it up to your PC and do it there.
Skipping backwards is pretty bad as it hangs for a while, then goes forward, and finally back without updating the screen. It makes replaying the last spoken line much more difficult than in should be.
Playback of photos is pretty painful and basic too.
I have focused on the negatives because that's what I want to know about when I read a review, but on the whole the device comes highly recommended, though there are surely newer devices offering a lot more now.
The unit is very quiet (depends on your HDD of course). Remote is OK (I've seem better and worse).