i am not a big fan of all-in-one dd carpc's.
they are usually a couple years behind the latest, and fastest tech, so speed is usually a issue.
there is also the driver support-- the all-in-one unit that used to be sold here is a great example of this--now there is no driver support whatsoever, and the parts are failing left and right, and people shelled out at least $2k for it not even 3-4 years ago... now, they can't even get drivers when the hdd fails...
i would highly recommend either building your own, or buying a prebuilt, standard computer motherboard-based system. the reason for these options is because, first, the hardware is going to be supported for way longer-- i can still get drivers for a asus motherboard built back in 2000..
the other advantage to building your own computer, is that when it fails(and it will fail eventually), you will have a better idea on how to repair it.
computers are really not that hard to build at all--i think that there are enough resources online, that it is almost as easy as putting together ikea furniture.