As a maker of boutique (I dislike that term) preamps, the basic difference to mine (or others) is being able to customize for the purchasers needs.As an example, I recently built a preamp for a fellow who wanted the tubes visible, wanted a specific coupling cap, and wanted a special color of faceplate. All could be done for him. As far as price to performance, often custom preamps can perform better than an off the shelf unit for less money due to less overhead.
Boutique/custom vs production tube linestages
There are many boutique / small hand made tube audio companies (ie. Aric audio, supratek, Tube audio lab etc). Have you ever compared one of these devices to production gear (ARC, VAC, VTL, Atmasphere etc). And if so what were your findings? I suppose the idea with these more hand crafted creations is higher value but I am curious about your personal experiences.