I've got both Mnemo's 3DO device and Deunan's Dreamcast device. They both work excellently. I will give the ease-of-use nod to Mnemo's device because he programmed a menu as well as chose to use USB instead of SD cards, but that's not meant to take away from Deunan's work.
I suppose the best I can say is: If either of these guys come out with any new product (and Deunan seems most likely to do it, he's actively talking about it whereas Mnemo just occasionally goes "SURPRISE BITCHES!" and pops up with a new one), I will buy it. PCE/TGCD, SCD, Saturn, CDi, I don't care.