It'll work fine.
There is no real difference between it being in a bike mount or not. The only issue is making sure the unit is exposed to the sky. My Forerunner works fine in a backpack or under the sleeve of my ski jacket.
BTW way, there are two Garmin 305 models. I assume you've talking about the Edge. I'd consider the Forerunner due to the wristwatch format.
There is no real difference between it being in a bike mount or not. The only issue is making sure the unit is exposed to the sky. My Forerunner works fine in a backpack or under the sleeve of my ski jacket.
BTW way, there are two Garmin 305 models. I assume you've talking about the Edge. I'd consider the Forerunner due to the wristwatch format.