I've had two pairs of these already and they work great. They do tend to run small, so if you wear a small glove, go for medium. The mitt itself does keep your digits pretty warm even without the glove inside. You'll only have to worry about getting wet if you have the vents open and if you tend to handle the snow often. The mitt fits pretty nice, but with the insert it might be a little snug for some.
I've had mine for two seasons already and haven't had any real issues with them as far as quality. However, my digits do get a little moisture from time to time. But that's probably just normal wear and tear. A good coating of waterproofing should bring them back to new again.
Overall... I see them as a 3/1 system mitt/glove combo. You can wear the mitts by themselves and stay warm. Wear them with the glove insert for the extra cold days or just wear the glove insert by themselves for spring time riding. For all that, I think they're worth the investment.
Oh yeah, I also like how it's a mitt and not a mitt with a built in glove. With your digits moving freely and touching each other, its easier to get and keep them warm.