My first bike computer had a cadence on it and I really did like it. I had to replace it a couple of years ago the rain in the northwest did it in. My new on is wireless which I love but no cadence and I do miss having it. I say if you can afford to get one do it you won't regret it.

As far as for shifting that's more of a feel thing, cadence just lets you know or helps you get into a good cycling zone and helps you push yourself harder, it is a good training device.

Happy pedaling!