Yep, i used the M6 for a long time and loved it until the F75 proofed to me that it is the better detector.
What i liked about the M6:
Selectable Tone ID (One tone or 7 tones),
Ground tracking switch (Beach, On, OFF)
What i didn't like was the angle of the grip, but Whites changes my M6 to the MXT style grip and that solved the problem for me.
Second problem is the 9.5 standard coil. That coil is way to large for a sensitive detector like that. I used it with the 6x4 DD coil and had good finds in trashy areas.
The 6x10" DD coil is a must have too.
It is a $699 detector that come with the wrong grip and coil. I don't know if Whites is going to upgrade it to the MXT style grip, you have to buy additinal coils (4x6 and 6x10 DD) to get the job done.
Then we talking about $900 to $1000 with the extra coils.
Now compare it to the F4. Right now you get it for $425 with three coils (11"DD, 8" round, 4" round). No extra coil to buy !
The F4 doesn't have that automatic ground tracking but it can be ground balanced manually in the auto tune all metal mode.
It won't beat the M6 on gold or other low conductive targets but it will do as good on silver.
The 11" DD of the F4 will cut better between the trash than the M6's 9.5" round coil.
The F4 has a better angle at the grip and a better feel.
The F4 is the better value, but if you're willing to spend $900 to 1000 to get the M6 to work you're better of to go for the F75 (like i did) or T2.
Hope that helps,
Andy,NM