I have a 305 and LOVE it. It looks bulky, but I don't notice it on my wrist and the screen is large, so I can easily view 4 fields at once and toggle between 3 screens.

Not sure about the HRM issue...I have honestly never even used the strap that came with my 305. One of these days I will, but the underwires in my regular running bras is what has been a deterrent. I'm not sure how to fit the strap around/under those and if I put it lower-on my ribcage I don't see it staying put.

If my 305 died today I'd probably buy another one...or maybe the 310XT, but I could buy like 3 305s for the same price.