I have a Readynas DUO V1 that is about to die. Which would be the best one to buy next? Is there a big difference in performance?
Yes, there are big differences in performance.
If a 2-bay unit is enough for you, then your choices are RN102, RN202, and RN312. All these products run the new OS 6 firmware, and all are a lot faster than your duo.
If you are fine with the functionality you have today, then the RN102 might be right for you.
If you want more (for instance, you are interested in plex, want to use > 4 TB disk drives, want to use the built-in antivirus feature, or just want the fastest file sharing), then uplift to the RN202 or the RN312. The RN200 and RN300 are fairly close in performance (its a big step up between the RN102 and the RN202, a much step up from the RN202 to the RN312).
Prices vary, but current Amazon US prices are
RN102: $119
RN202: $287
RN312: $414
At those prices I'd personally go for the RN202 over the RN312. But if the gap is < $50US, I'd likely go for the RN312.
