Here's some more info on the Boost D.L.A. from Tech 21

Tech 21 brings a fresh perspective to the standard delay pedal. By incorporating a clean Boost function, up to 9dB, your solos will jump out with greater dimension. The Boost D.L.A. is designed with user-tweakable, “lo-fi” analog technology. By manipulating the controls, you can infuse degrees of warmth and life characteristic of vintage delays. The circuitry intentionally injects the inherent imperfections of vintage units, which is what makes them so seductive and nostalgic. A single, continuously-variable Time control provides a full sweep, up to 1000 milliseconds, of delay. The Boost D.L.A. parameters are engineered so that you can explore and custom tailor such delay styles as digital, vintage tape and bucket brigade.

Tech 21’s Boost D.L.A. with Tap Tempo offers an abundance of easy-to-use, intuitive controls in an incredibly compact pedal -- and it’s battery operable, to boot. All of the features are truly useful, not simply a bunch of clever ploys that are overkill and that you’ll rarely, if ever, have a need or desire for.