The bigger coils do cover alot more ground but if theres trash you will get multiple signals also they will go deeper on bigger targets but you will lose depth on smaller targets because the way the coil works . Ive had the big coil and many others I know have also they can be great depending on wwhat and where your hunting plus you need to ground balance them at half or lower sensitivity..HH Truth
A2 your information is spot on regarding big coils in general but I have to beg to differ with you on your ground balance statement. I cannot speak for all other detectors (though I have owned many different models from most of the major manufacturers), but as far as Equinox is concerned - there is no need to lower (or raise, for that matter) sensitivity to properly ground balance ANY of the Equinox accessory coils. This is not stated in any Equinox instructions or in books or online information officially endorsed by Minelab (including Andy Sabsich's latest book which contains settings recommendations by yours truly).
Also, if you think about it, this would not make sense for the Equinox design specifically because that would mean tracking ground balance would only work properly with the big coil if you were operating at low sensitivity and that is simply just not the case.
Now, I know that under certain conditions, manually setting up ground balance independent of what is indicated by the manual, auto or tracking GB algorithms (called biasing) can be advantageous in some situations, and I plan to do some detailed testing at some point to see how different manual ground balance settings affect certain targets under certain conditions, but sensitivity adjustments to perform ground balancing are simply not required. GB should still get set properly even if you do lower sensitivity, so no harm done, I suppose, if you do this, but it is unnecessary and any time you can avoid unnecessarily tweaking settings means less of chance you will get the machine in a bad configuration requiring a reset.
Regarding big coil sensitivity on small targets, big coils do "lose" sensitivity on small targets in general. I have found, however, the Equinox 15" coil seems to suffer much less from this than most "big coils". I have recovered some tiny targets with the big coil including percussion caps and earring backs in low density target situations, so Minelab has done a pretty good job on the design of this coil preventing small target desensitization. However, like most big coils, it does suffer from target overload desensitization in dense target situations (or high mineralization) so in those cases I would opt for one of the smaller coils.
HTH