I've had the scangauge
, a bluetooth adapter hooked up with the Torque app on my phone, and now have the Ultragauge. Of those 3 options I'd recommend the Ultragauge every time.
The Scangauge is good but nearly twice as expensive as the UG and it only shows 4 pieces of info. The UG shows 6 pieces of info on a single page and you can program up to I think 7 pages with info, so you could potentially have 42 different gauges. The UG screen also looks better and it's easier to reset when you fill your tank.
The bluetooth/Torque app combo worked OK but (for my phone at least) I had to re-enter the bluetooth code every single time I got in the truck and Torque would eat my phone's battery. Overall it just isn't nearly as easy or convenient to use as the UG (just plug it in and forget it.)
There is a thread on here with a sh*t ton of pictures of mounting locations for the UG. I don't have a picture right now but I ended up putting it behind the steering wheel on the column. It partially blocks the lights on the left side gauge but it's easy to see and still out of the way, plus the wire is hidden in the steering column.