I have the C3 nailer and I love it. Sure a pneumatic is cheaper and lighter, but for the occupational work where you don't want to have to drag air hoses, let the compressor build up air, etc, etc... You can slap in a battery, choose you nails, and go...
It has two adjustments for depth, typically I have no issues with it driving flush unless I happen to hit a big knot in the wood, then usually a couple hammer taps will get them down. Never had mine jam either. Only downside can be the bulk. I've had a couple times where I couldn't get a good angle, but I made do. I don't find the weight an issue. It drives nails pretty darn quick, probably 1 per second.
But for the portability options. I've had projects in my backyard where having that little nailer made life so much easier. If I had a pneumatic it wouldn't have worked because I don't have enough air hose to go from my garage, around the house, and to the back... Also I've taken it to a friend's house a couple times for projects...