Designed and sold especially for bicycling. It fails because it's basically a single layer of insulation, not as warm as a mitten, and not sized well to wear another layer over or under it.
REI's "Back Country" glove. It seemed promising. I think it uses a three layered design, while still feeling flexible. It still lacks the insulation of a mitten, serious wind blocking, or the ability to layer well.
A wool convertible mitten. I haven't had these long, but they seem like a nice general purpose cool weather cycling solution. These mittens fail on their own to provide serious wind or water protection. Next I would get enforced thumbs to prevent shredding them from velctro exposure.
This "overmitt" overs light insulation on its own but blocks wind and water well and is designed to allow smaller gloves or mittens to fit inside it. Combining it with with the wool mittens are super-warm, while other combinations can be used when less insulation is needed.