Winding, I have had the 405 for over a year now and use it for both running and cycling. I have the footpod for indoor running and the cadence monitor for cycling. I like the fact that you can use the same training device for both activities and can download it into my training center on the computer. The only thing I don't like about it is that you have to manually change the modes from bike to running so you can't use it during a triathlon or biathlon without losing valuable time. It's not that big of a deal once you learn how to change the modes. There is a bit of a learning curve with it but since you already have the 50, this shouldn't be a big deal for you.
My husband had an extra hrm with his Garmin and I used it when I got my 405 and it paired just fine. We have 3 different Garmin's between us and they all use the same hrm.
Hope this answers your questions.
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"We don't stop playing because we grow old; we grow old because we stop playing." George Bernard Shaw
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