Treble boosters really shine when they are used on tube amps.
Guitarists start to use them in the 60's to make their guitar cut better through the mix. The old tube amps where dark sounding, especially when used with a Les Paul or ES 335. By using a treble booster it was possible to get a brighter sound.
A treble booster will cut the low end of a guitar sound and increase the mid and treble. It will push the preamp into more distortion. Rory Gallagher used it a lot.
Dallas Rangemaster is a famous treble booster from the 60s. Keeley Java Booster is a good treble booster. Today you can buy lots of different treble boosters.
TAD Range King is an interesting booster because it can be used as a treble booster or clean booster. That is because it is possible to ad or lower "balls" (bass)
You have to try which booster fits you and your gear. If you want to try a cheaper treble booster you should check out Electro Harmonix Screaming Bird.