Hot Head Coils

I normally say 'Hot Shot' good, 'Hot Head' bad.
You don't say what machine you have. I found no depth increase with the 12" on the Whites 6000 Di Pro Sl, Spectrum, or XLT (XLT has its own version). In air slightly better as you would expect from a larger coil but in field use sensitivity had to be reduced to maintain stability.
The 10" acted much the same on the Master Hunter CX Garrett but, roll of drums, having written them off as a bad bet I met someone with the 12" that he used on his Fisher 1266 and he was getting extra depth.
Don't know if you saw Carols posts (yesterday) re her trying a larger coil and finding really only increased scan width but its a pretty common result. Lately they have been bigger coils that do manage to add performance, detection width and better pickup on coins on edge and with little or no weight increase. Bigger they are the better they have to be built. SunRay, Coiltek can pull it off, others can't. One cheap brand has the coil windings glued on to corregated cardboard.

I agree with Brian. Most after market , made for one detector dealer accessories are not very good. The steep discounts should tell you something right off the bat.

My only experience was with a Garrett Master Hunter CXII, very eratic, little or no increase in depth. I now stick with coils made by the detector manufacturer.