The Dewalt attachment works with the FS guide rails. I have one somewhere, but don't tend to use it. Instead I butt the guide rail to a Woodpecker square or a shop made (2" by 1/4" aluminum bar stock) T-square.
My only issue with the Dewalt was that the 90 degree "leg" was somewhat short, limiting accuracy.
Not even sure it is still available:
http://www.amazon.com/gp/product/B001J34IQ4/ref=wms_ohs_product?ie=UTF8&psc=1
RMW