R600 is discontinued. It was in the same line as the R700, they are basic 6 and 7 channel rx.
Either one of those rx will work, but the R600 is used (no doubt) so make sure you check it out thoroughly, or send it in before flying with it. Same goes for any used rx. You can also use the dual shift rx from hitec, I used those all the time when I was flying 72 mHz