Mittens are warmer than gloves, but mittens are less dexterous than gloves. Manzella is a handwear and headwear manufacturer that is attempting to overcome these inherent deficiencies by changes in physical design and the use of new materials. The mitten covering the fingers pulls back and exposes a half finger glove.
Velcro secures the mitten to the back of the glove, keeping it out of the way.
The thumb can also be exposed in the same manner as the fingers. The thumb flap has no velcro, but doesn't seem to be a necessary feature. The palm also has a Grip-Tex palm. Grip-Tex is a sort of roughened synthetic leather that aids in gripping. The Z-Fleece Ollie would make an interesting shooting glove for above freezing temps.