I do a lot of indoor rowing, during which the optical HRM on the Forerunner 45 is about as useful as a chocolate teapot (this is the same on all wrist worn optical HRMs - they don't really work when rowing)
So after investigation, I decided on ordering a HRM Dual. It is one of the few chest straps that can transmit R-R timings over ANT+. However, the Forerunner 45 does *not* support this over ANT+! What are the chances that a future update to the 45 will offer full support for the HRM Dual? It would be nice to get stress readings whilst rowing, as well as when I'm running and using the internal optical HRM.
Therefore, unless the Forerunner 45 is updated to fully support it, don't bother buying the HRM Dual for use with the 45, it's a waste of money - may as well just get a generic ANT+ HRM chest strap instead.