I believe I mistakenly sent out a few devices with a version of the firmware that requests too much power, which can problems on iOS devices (iPad, iPhone). If you get an error when you plug WARBL in saying that it uses too much power, I'll ask you to reinstall the newest firmware, available on the Documentation page. The bug doesn't affect the actual power that WARBL uses, just how much it requests, so it will operate normally on Macs and PCs.
Sorry about that!