For about two years, well maybe even three I was cycling with a VDO speedometer. Unfortunately one day this year the speedometer stopped working. I decided to buy a Polar M450, which not only shows the speed, but the pulse and more.
I chose Polar M450, because the M400 that I had before turned up to be a nice product. Only it wasn't always convenient to check the display while having it on my wrist. Of course like the M450 it can be fastened to the bike, but you need a separate holder for that.
After the first ride I can tell that I like it. Only the display feels "slow". Also the speed parameter takes a little to update, because it's calculated using GPS. The pulse, like with the M400 is measured using the Polar H7 chest belt.
I like the ability to customize the display of the M450, the same as with the M400 it's done easily using the Polar Flow service. Using different sports profiles you can pick four parameters to be displayed. I currently ride with these parameters: current pulse, maximum pulse, speed and the distance cycled.