Be aware that 230 calls for chest strap and 235 have built-in sensor to the wrist. The product seems to have some teething problems. It was a little book to pair it with your heart rate belt. Late la sync to the phone after a few days. Both of the stuff was pretty easy to fix, but it cost some time.
The clock is easy and feels plasticky. On the positive side a good display, simple and clear menus and no problem getting it to show what you want. Good battery life and I think GPS tracking is more accurate than my old 305. It may also prompt contact with the heart rate monitor and GPS.
On the whole, I am satisfied, possibly maybe I should bet on a 235, but at the same time one knows that the chest strap works stably and accurately. I'm not sure that a wrist sensor does.