Garmin owns ANT+ by virtue of buying Dynastream Innovations, which organized the ANT+ Alliance. Apple, of course, has many engineers on the steering committee for BTLE. What this means is that even though Apple's hardware contains ANT+ compatible antennas, Apple will never support ANT+. (Interestingly enough most Sony phones actually support ANT+, since Sony doesn't care enough to disable the support) Similarly, even though many Garmin devices use an SOC that support BTLE, Garmin deliberately only enables bluetooth for phone connections.
In practice, what this means is that you're committed to ANT+ if:
- You have sunk thousands of dollars into ANT+ power meters. (newer power meters will also presumably support BTLE)
- You have plenty of legacy ANT+ hardware that still works (e.g., old Garmin computers, watches, etc)
- There's an ANT+ sensor you care about that doesn't have a corresponding BTLE version. (e.g., the inertia-based speed/cadence sensor, which are miles better than the magnet-based versions)
- You have a need for a single transmitter going to multiple head-units, which is something that BTLE doesn't currently support. (BTLE currently only supports Star network topologies, so only one head unit per slave)