The Garmin C-series are a tiny bit smaller. The i-series are about half the size. The screens on the i-series are way too small IMO.
The external antenna needs to be mounted with a view of the (southern) sky in order for it to be 100% effective, but the unit picks up the GPS signal pretty well even when the direct view is obscured (it's about 50% effective in the storage bin).
Right now, I mounted a magnet under the dash to place my GPS antenna when I'm using it. When I'm not using the GPS or when I'm parked, the antenna sits in my storage bin so no one will know that I have a GPS in the car just by looking inside.
