I have used both RAM suction cups and prefer the locking suction cup. They're cheap enough to where you can buy both and interchange them.
The locking cup has a smaller diameter and is a bit easier to remove. Though I usually don't leave attached to a hot window, I'm not sure what the long term effects of heat are on the suction cups.
I have found that temperature changes and a dirty interior windshield will cause the seal to break. Also keeping the surface of the mount clean helps, too. A little moisture helps keep it stuck, slobber works.:drool:
And yes, the Ram Mounts don't come with power cords but should be compatible.