Kaiser's kit is extruded; I just replied to his post. OTOH, $55 is a lot less than I paid for cast acrylic to build the sump for my 45 breeder....

I'd definitely go for an undertank sump, regardless of whether you use it as a refugium. You can add at least 10 gallons to your system, it makes water changes/treatments/etc much easier, and your tank will look way better without stuff like a heater in it and without the scum on the surface.