The Lumicon 1.25" Multiple Filter Selector with 3x3" Base is essentially a combination of their standard 1.25" filter selector mated to their LH2000 low-profile reflector focuser.  It accepts 1.25" eyepieces and has a built-in sliding tray which gives users quick access to up to five 1.25" filters.  It is very common to leave one of the 5 slots open, so that you can compare the naked view/image with various filtered views/images.

Typically with Newtonian reflectors, adding the standard Lumicon 1.25" filter selector adds too much path length to achieve proper focus because they don't have much 'in-travel' upon their focusers.  So they've come up with this adapted solution, which remains very close to the body of the reflector tube to eliminate focus path problems.

Beyond the benefits of the filter selector, the built-in helical focuser here is incredibly refined and enhances both visual and imaging use.