I have noticed that once I use a coil smaller than 8 inches, in the farm fields I hunt and many parks for that matter, I start loosing too much depth. Don't get me wrong, I love my excellerator 4x7 and my 6 inch excellerator and 5 sun ray, but they are not really pulling much below 6 inches and with corn stubble that might drop down to 4 inches. Awesome separation, but if your average targets are say at 7 or 8 inches and you are using smaller coils, you probably won't here them unless there is no other targets near them in clean ground, in which case they would have been easy to pick up with a Sun Ray 8 or the 11 inch pro.
I am definitely interested in this size 8x6 SEF of this particular coil because maybe it might get near the depth of my Sun Ray 8, one of my most favorite coils I own, and get slightly better separation because of it's narrower width of 6 inches. I am going to order one this week.
I personally disliked the SEF 10 x12. For me it was way too heavy for it's size (felt like I was swinging a 15 WOT) and did not get the depth or separation of my 11 Pro coils, so I just never saw any benefit of using it instead of the Pro coils. As far as I am concerned, you can never own too many different size coils as each different size or shape coil may just be a perfect fit for a specific area of any given site.
The only thing I would add to that is that some coils overlap each other in performance and size, for me the 10x12 SEF was an overlap of my pro11, so I felt kind of wasteful in the SEF purchase. That's the same with my SR 12 and Excellerator 10 x 14, having the Excelerator 10x14, I didn't really need a SR12 as I get better depth with the 10x14 and seem to get better separation. Same with the ML 8 and SR 8, my SR 8 got better depth, better separation and was lighter than the ML 8.
I finally got a 5x10 Coiltek coil last spring or the spring before and hated it, James in ND used it and was just smashing them with it on his EX1 or 2. On my SE's, anytime there was iron near, not under the coil, the machines would false high silver causing me to stop and investigate only to find out it was an iron false, not silver. This would happen constantly and drove me mad. I sent it back to Doc and he sent me a new one which gave the same results. It could be possible that 5x10 coil was tuned specifically for the EX 2 rather than the SE, I don't know, or maybe having the SE with fast on and that coil combined gave too much iron falsing, I never got to the bottom of that and I really wanted to because the size 5x10 seems really intriguing to me for sites with dense trash and also 8 inch average depth coins.
Then there is the last monkey wrench in the whole thing, in that some coils are not tuned perfectly and you might use them, not like them and put them on a shelf and wonder if the guys posting positive results about them are full of it or don't have a clue and the entire time, your coil could be bad
. That's why I own two SE's, so if something is queer, I can kind of pinpoint it before I waste several days thinking my machine is wacked.