Yes, I have a Scangauge II installed. It works great. It plugs into the DLC and is velcro'd to the top of the steering column. Haven't had a single problem with it and the instantaneous feedback is priceless. Highly recommended.
I'm not familiar with the ecometer, so I can't compare them.
See my thread here.

Question: do you have & use a SGII in your Vibe? If yes, how does it work? Well, troublesome, or what? I've got an Auto Meter ecometer and although it does work, I'm not really happy with it.