The biggest issue with Bluetooth & the QED isn't lag time but the QED/QED audio doesn't seem to like most Bluetooth so audio quality isn't good. Good quality & low latency Bluetooth on most devices has very good lag times & in comparison to other RF systems can actually be superior or just as good nowadays.
All RF systems need initial pairing but this is usually fairly easy even with Bluetooth. Some proprietary systems (including some Bluetooth) come pre-paired.
Bluetooth is just another proprietary RF wireless system with different proprietary operating codecs etc. like the Minelab, Garrett, Quest & Seinheisser (Kleer) systems so not sure why others can work better over Bluetooth? Downside is Bluetooth is by far the most popular system for compatible gear.
I have heard recently that steelPHASE has been trying to work through similar issues with the QED audio & the steelPHASE SP01 enhancer? I.e. the audio quality doesn't improve much through it? Maybe Pat can clarify here?
My own testing showed that the SP01, along with other enhancers, were largely ineffective on the QED using wireless systems. I am led to believe that this could have been due to my using good quality higher ohm headphones/earphones (usually recommended for detecting) whereas lower ohm headphones/earphones work better with the QED.
Anyone I've seen have good results with Bluetooth on the QED seem to be using low ohm earphones like those supplied with mobile phones.
Hopefully someone successfully using Bluetooth on the QED might comment here as Bluetooth does open up a lot more wire free options where it's usable.