I think I can help a bit here. The "Detech" "SEF" and what have you...All are talking about the 12x10" Detech SEF coils. Some call them 10x12 coils, but the technical description is a 12x10, made by Detech, sold by Findmall as the official US outlet and Find Mall sponsor, and are called "SEF" coils.
There is the 8x6, 12x10, 15x12, and several other larger sizes of these unique coils. However, most seem to prefer the 12x10 in terms of maximum depth on coin/ring sized targets and still excellent left/right separation.
Far as handling rough ground or iron...Yes, on the FBS and BBS machines the SEF coils have a reputation for handling rougher mineralized ground or heavy amounts of junk iron while running smoother, which is a feat in it's self since Minelabs are known for doing that in the first place. They also seem (by my experience) more sensitive to smaller targets, and also have the ability to run at higher sensitivity levels not only by seemingly handling the ground matrix better, but also by seeming to be less prone to EMI.
They are unique coils unto themselves, and I'll dare say that at least for me the 12x10 is the best DD coil I've ever used in terms of depth, stability, and smoothness, along with pretty much all other aspects of coil performance in a coil roughly of that size.
There are some though who still prefer the Pro Coil over the 12x10, so my advice is to
most importantly read Bryce's field reports of various coils, as well as to search this forum for various opinions on various coils and draw your own conclusions from there.
Like all things in life, not all "advice" is the same, or of the same results for different people in different situations (soils).
I can only tell you that I've dug into the deep dark corners of the net reading extensively on coils for both the FBS and BBS machines, and contrasted that with my own experience with various ones, and have arrived at the conclusion that the 12x10 almost never comes off my land rig, unless I'm putting on a tiny trash coil for the odd very worst of trashy situations, of which most of the time I'm confident the 12x10 can handle most of that in terms of left/right separation, but of course in terms of the length axis smallest is still best IMO when you just have to sift through the trash by mere inches at a time length wise.
Most importantly I'd tell you to read Bryce's extensive field reports on the various FBS coils, because that is a solid foundation to form choices or opinions on, and contrast with what else you might dig up from others on your own, but the smart gambler will pay very close attention to what Bryce has to say for a FBS machine...
PS- One other item of note: I've got soil that spans from moderate to heavier minerals, and I can tell you I've used some very good coils and machines in my day in it, but the SEF coils set the bar a good bit higher in terms of what I expect now. I've read results, but more importantly I've seen and heard with my own eyes. I won't bore you with what I've seen the 12x10 do for me in both depth, separation, and stability on my machine, but I will say that if another coil comes along to replace it it's going to have to dig the coins up for me on it's own to prove it's a worthy replacement.
You might also look into the very new 13" Ultimate coil that is also made by the same company (Detech). While it might not be a replacement for the 12x10, many seem to think it has some unique qualities all of it's own that makes it worthy of consideration in a line up of larger coils for a machine.
Bottom line though is to read Bryce's field reports on various coils and decide from there, because the same coil on different machines can have very different performance characteristics. Not all coils are a good match for all machines, so if you want to hear "the final word" on a coil for your Explorer, then look no further than what Bryce has to say. He's done a great service to the Minelab community, and his expertise on coils is legendary by all the experience he's had and reports he's done on various coils for the FBS models. Read his reports and you'll have a good idea of just what to expect from various coils, or in this particular case the SEF coils...