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So, the Nexus 5 does have an Ant+ radio, but it's disabled by default. If your phone is rooted, you can use BT Patcher with the Ant+ Enabler Plugin to turn it on.
That said ... I currently use the Wahoo Speed and Cadence Sensor, which is compatible with Ant+ AND Bluetooth 4.0. I am currently using the BT connection because it works fine and doesn't require any hackery. If I get a phone that supports Ant+ without hacks, I'll probably switch to that.
However, the one real advantage of this Speed & Cadence sensor is flexibility. I currently use it with my phone and a rflkt. But I could decide to get a "traditional" Ant+ head unit, and still be able to use the sensor.