I've used it on the indoor trainer w/ zwift, no problem, but it is like 8 button presses to navigate the menus to flip it on. Not something I'd want to do while riding out of T1.

Also I don't know how much power it drains in that mode. It is not a tri watch, so the battery might not hold up for the entire bike+run.

Edit: also to your question - during the bike, your 235 would broadcast HR but you don't start an activity on it. Start the bike activity on the Edge. Save that when done. Then start a normal run activity on the 235.