That's a great deal Greg! "Estimated Delivery Date: Aug. 12 - 28 when you choose Standard at checkout." I just don't understand how any standard shipment will take that long. They must be building them to order in China and walking them to the container ship.
Here is MPJA's version.
http://www.mpja.com/Pulse-Generator-Board-Adjustable/productinfo/31070%20MI
Of course, these all should be called rectangular wave or pulse generators, and not square wave generators. You can always double the frequency and follow the output with a JK flip-flop like a CD4027 if you need square waves.
Joe