Very Reliable
For me at least, the CS 100 has never put a foot wrong and is very simple and easy to use – a lot more than can be said for the 705 which is a hobby in it’s own right!
For me the fact that it is a watch rather than a committed bike computer is no benefit with the CS300 and it doesn’t offer any other benefits in performance of note against the CS100. But for you the fact that it can be used for other sports as an HR watch may be of real value (for that read “I don’t do anything other than cycle”)