Geometry Shell doesn't work as advertised.
I have a bit of a bone to pick concerning the Geometry Shell.
The official advertising for Daz Studio 4.5 lists Geometry Shell under it's features, as well as a description of what it's for.
DAZ_bfurner said:5. Geometry Shells - This new feature helps blend the textures, shaders and geometry of Geo-Grafted parts to the figure. This will provide a much cleaner feel to grafted geometry.
The problem I have is that it's actually impossible to do this with Geometry Shells, leading me to believe that nobody at Daz actually tried doing this for themselves before writing this.
You see, the Geometry Shell shares the exact same UV map settings as the base figure you're using it on. If Genesis is set to M5 uv maps, the Geometry Shell will also use M5 uv maps. Same with V4, V5, Hitomi, etc. You can't use separate UV settings on the Geometry Shell.
This makes it impossible to "blend textures" between geografted segments. Let's use the M5 gens as an example (as the V5 gens doesn't have this problem). The M5 gens requires it's own separate texture, one that matches the torso texture, in order to blend in. There are very few character packs available that contain matching M5 gens textures, so naturally the ability to blend between the two (similar to how the M4 gens could through an opacity map) would be very useful.
You're supposed to be able to use the Geometry Shell to blend between geografted areas, but because the Geometry Shell will still have the exact same UV map settings as the base mesh, this isn't possible, it would still look the exact same as before. The only way you could actually blend between those areas is if you created a new, compatible texture, at which point you're getting the exact same results as you would if using the Layered Image Editor.
As it stands right now, it's impossible to use Geometry Shells for their advertised purpose, unless there is a trick to it that Daz isn't revealing to us. If that's the case, I would really appreciate it if someone from Daz could actually walk us through how Geometry Shells are supposed to help us blend the textures of different segments, and exactly how it's supposed to make the geometry look cleaner, as I am genuinely confused by this.