I have never cared much about that frequency thing, under normal conditions on standard sized targets and depths most any frequency seems to work fine or always has for me.
With a 5.9kHz F2 I have found tons of gold including some very small, tiny rings and using my higher frequency Vaquero or F70 I have plenty of silver in my collection including small pieces of jewelry and many dimes...some found pretty deep.
It is in those not so normal situations where specific frequency ranges can matter.
There is a reason gold hunting machines are such high frequency units, when you are looking for tiny nuggets in difficult dirt...especially deeper.
Many use Fishers, Teknetics and other brands and do find gold nuggets too but for those hunters that are totally serious about it they spend thousands on the top end high frequency Minelabs and never bat an eye.
They aren't stupid to spend that money, they just want the best shot possible to find everything they can.
The right tool for the right job.
For finding silver coins fairly shallow most any detector works, if you are looking for the deeper and sometimes more challenging and hidden or masked ones lower frequency can penetrate the soil a bit better and maybe...maybe give you a slight edge.
They make detectors in all kinds of frequencies, some brands have low frequency optional coils and some are multi frequency...and they all sell well.
Again nobody is buying these things because they are stupid, this is about physics and low frequency tools have been proven to find that more difficult silver deeper by many so it is a true thing...whether everyone needs to worry about this stuff is another thing.
I am not buying an Omega with a low frequency coil or a FBS or BBS Minelab just for the chance to find one or two extra silver coins where I live and hunt...if that would even happen.
I seem to do pretty good with my higher frequency Fisher even in deeper targets and I have friends that are very successful with their AT Pros and a friend that has an E Trac doesn't really find all that much silver than we do.
If I lived in the NE. with all that history and I hunted totally scoured parks looking for the rarer deepest hidden silver coins I might think differently but for my situations and hunting sites frequency is just a non issue.