I order me the Wahoo cadence and speed sensor, the non magnet ones. It can do ANT+ and BT at the same time. I just bought me a Garmin 520 and will try out the ANT+ and Runtastic Bike Pro on my phone using the BT and see how things goes.

I have look at cell phone clamp on bike. The only one where you do a quarter turn snap on cost $50 with the case and the clamp. WOW! And its for the Samsung S6 or S7.