I suppose that would depend on exactly what you want to track. If you wanted to really keep track of things and analyze all your data then the 710 would be cool. I've seen some of the stuff it can do and it's really neat, but that may be overkill for you. My husband has a Polar S210? (I think) that he can download into the computer and his inner geek enjoys that, but he also uses a coach. As for me, I've got an M52 and I do keep a spreadsheet with the data from it and my bike computer. I look at it some just to see how I am progressing, but I don't feel the need for graphs and charts. Sooo, all that to say if you just want to see what your cadence is while you are riding and you don't want all the techno bells and whistles, spend the $30ish on a computer. Just remember to get one that attaches to the rear wheel if you ride the bike on a trainer.
Just my .02