In this particular review (again, I wish I could find it), the guy said that it pairs easily with all apple products. But if the iphone is in range, it will keep trying to switch back to the iphone, rather than sticking with what you've told it to (your iPad, or MacBook, or whatever). If you are out of range of the iPhone (say, out on a run with your watch), it works fine, but as soon as you're in range, it will switch back to the iPhone.
As you say, however - this may be why they've delayed the additional W1 units.