Cibola does well across a fair range of conditions with the fixed ground balance. Pre-mod, mine had a positive signal response in all metal when lowering the coil towards the ground in nearly all conditions I encountered. The places where a lot of depth was lost were places like ball fields where the red clay used for the infield was also all throughout the outfield or some of the gravel parking lots (depends on what was used for the gravel; lime stone not bad at all, slag or granite chunks are a different story). The ground balance mod allows a bit better depth and response in those tough conditions. It doesn't get you the 9 to 10 inches you get in mild soil but in the tough conditions the mod can get you an inch or so more over stock when you adjust properly.
The detector design does not allow it to be ground balanced to wet salt, so for salt water beaches, the mod does not help for the wet sand areas. For most dry sand areas, you don't really need the mod.
If you like to tinker, go for it. Be aware that doing this mod will void the warranty.
Cheers,
tvr