Well Simon, there will be many who don't agree with me (nothing unusual) but like Norvic I don't use them these days. As pointed out by a well known Australian prospecting personality, boosters cannot create a signal that the detector has not already recognized and audibly responded to.
In earlier days of the VLF detectors, some had a volume that seemed a bit soft, so signal enhancers were widely used to boost the response, however the latest generation of pulse induction machines have more volume control, and generally do not require further enhancement. I prefer to have noise reduction to eliminate distracting outside sound, and even 'white noise' that is not even noticeable until noise cancelling is switched on. Most of the WiFi systems, which I favor have, have a volume control, with the Sennheiser system having volume control on both the transmitter and the headphones. (These H/phones are not noise cancelling, but very good) With TX volume control and N/C I find I have as good a clear and unobstructed audio as I could wish for.
It's a 'different strokes for different folks' scenario, and I've had situations where I have picked up a mates detector to have a listen to an uncertain signal he has picked up, only to think, "my God how can he run a machine like that?" Threshold way up, with the machine 'screaming its tits off', the pitch so high its deafening, and running a booster as well. The perfect way to go deaf. Maybe some people are partly deaf and need a booster. The way I like to run is with threshold only just there, tone way down low, noise cancelling on, and cordless.