a standard 250k or 500k volume pot inconjunction with the cables capacitance creates a corner/cutoff frequency that may or may not cut some high end in a typical guitar wiring scheme. the idea with a preamp/buffer is to change that high impedance output to a a low impedance so that the corner/cutoff frequency is well out of the guitar frequency range.
the blaster has a low impedance ouput, so placing it after the guitars volume pot isolates the cables capacitance for no loss. that is where it is designed to be. but when you place the blaster, or any of the preferred preamps, before the volume you want to change the volume pot value to 25k which is a low enough impedance to also isolate the cable capacitance for no loss. wiring in the latter fashion and staying with the stock 250k or 500k, while definately useable, only negate any of the benefits of the preamps low impedance output benefit.
Disclaimer: I make and sell Buffers. I also sometimes Modify, Build and sell preamps and amplifiers. My opinions are not intended to be sales pitches. I am a one man shop and prefer to spend time with my wife and family, i work full time on call and love to spend my spare time doing other things. I only make, modify or build things for those that seek them.