I purchased the SEF 12X15 from Kellyco 2 weeks ago. It is definately longer than it is wide. While I haven't measured it myself, I think it is safe to say that it is 12" wide and 15" long.
If you are in the United States you'll want to purchase it from Kellyco, in Europe, I suppose you would buy it from
Joan Allen. I am pretty sure the Kellyco and the Joan Allen coils are the exact same. Based on the availability of 18"X15" and 21"X17" at Joan Allen, the coils are were created/manufactered there. My Kellyco one has something to the affect "Made for Kellyco" on it.
However, even if you are from Europe you may want to check out the exchange rate, 1 British pound = 1.8652 U.S. dollars. Kellyco may have it cheaper. I believe I did the calculations prior to purchasing my 15X12 coil, and the JoanAllen one would have been $100 more.
I like mine so far, I can cover a bunch of ground with it, know I'm probably reaching deeper. I can pinpoint fairly well with it.
Jai