I think it is unanamous! I have the gl*******s kit too - mine is 2 x 2" bulkheads, box has teeth. IMHO, it is one of the truly great bargains in this hobby. Yes, I know you have a drill bit for the hole(s) - is it the right size to match the bulkhead(s)? Also - a single drain can fail. even if nothing crawls in to it, buildup of gunk will slowly constrict the inside, reducing flow.
FWIW - my 150 has a total of 4 drains - 2 x 1" with corner boxes,(put in when overflows were a "new" idea, circa 1990, and the 2 x 2" gl*******s kit installed in the center of the tank - My return pump is a dart that also feeds the refugium (a 120g) and my GFO and Carbon reactors (2 x single BRS)