See there are two different things:
1) The manu-matic type things, which are basically an automatic transmission that you can control. These have little/no gains, actually most of the time you lose speed.. plus you still have the drivetrain loss and big weight difference.
2) The true clutchless manuals, found in a few HIGH end cars. These have a clutch, flywheel, all the good stuff.. so they don't have the drivetrain loss of an automatic, its just a manual transmission that uses hydraulics rather than your foot. However.. you still have alot of weight added.
The clutchless manuals (#2) aren't bad (I still wouldn't want one) but are most likely ALOT more expensive. Its not as simple as just controlling your automatic, like #1.