Jerry Lodriguss has written a review of the SFF7-2 flattener when used on the Stellarvue SV70ED scope. He compares the performance with an Astro-Tech 2" (AT2FF) flattener and the "William Optics 0.8x combined field flattener / telecompressor", which could be the WO flattener 2 (or perhaps an earlier model?)
Jerry's review is here
http://www.astropix.com/HTML/I_ASTRO...STS/SV70ED.HTM
There is also some relevant discussion here
http://www.cloudynights.com/ubbthrea...sed/sb/5/o/all