We have one. it's wonderful, stowable as you describe, and a lot of fun to glide around silently getting up close and personal with the shore birds in a way a noisy, heavy RIB just can't. Ours has the added benefit of a clear bottom, so we can look right down at the fish as we go. The practical reality is that it's a PITA to inflate just to go ashore, though, and quite a struggle to travel in any kind of wind or current (compared to a good quality hard kayak). We think of it as more toy than transportation...but wouldn't go without it.
That said, we haven't needed the "second car" option in our cruising yet, we tend to just spend all our time together. (Saccharine, isn't it?