Aah, yes - I recall you asking questions about the shampoo bottle in the Carrara forum:)
Did a quick mock-up of it in Hex to see where to place the seams and pins - you can see from the first pic one of the major reasons I don’t use hex for UV mapping - see the tiny dot in the bottom right corner? That is the bottle top! Hex has no sense of proportion because it forces the whole map onto the grid.
You can imagine what it would be like trying to eye-ball manually correcting proportions with a complex model!
The second one shows what it looks like in UU3D, after setting auto proportions.
The other two reasons is that it doesn’t retain seams and pins after saving and re-opening, so it has to be a single-session operation and secondly it is inclined to crash when doing complex mapping.
Other than that, it has a pretty good UV mapping and manipulation capabilities:)