Other things to consider are:
Is the screen easily readable?
Are the buttons easy to use?
Can I upload the data to my training log to store, manage and analyse my training? (Polar watches only work with Polar software, whilst Garmin has it’s own training log software – Garmin Connect – but still allows you to upload your data to other training log programs)?
Do I want to be able to measure changes in altitude?
Do I want to be able to use it as a normal watch?
Do I want it to link with my power meter/heart rate monitor?