I play with it some on my phone, haven't been on any significant trips lately so I haven't settled on what I think is important to monitor.
Right now what I think is more important to keep an eye on is engine coolant temp, and battery voltage. I have gauges on my dash for these, but those gauges are range limited, meaning the needle just goes to the middle if it's within tolerance, I can't tell if something is rising or falling until it's already went out of range. I also just like having actual numbers instead of needle positions.
I need some kind of extra programming to make it work on a Nissan but if I figure it out I'd like the On/Off indicator for the electric engine fan. Might be a useful reminder for a water crossing.
I think it works well but I think I would get more use out of it on a tablet. My idea is to eventually get an Android tablet, and have a mapping app up, then use the dashboard plugin to overlay a engine coolant temp gauge. I'd also set some alarms so if I'm off pavement it will yell at me if something is starting to go amiss.
Oh, from what I hear, don't cheap out on the BT adapter. I got one of the better ones for like $30-$40 and it works smooth, the lag is minimal. I mounted it under the dash with zip ties so anytime I'm in the truck and want to access the engine info I can just pull out my phone, links up on it's own when you open the app.
Here is the panel I use on my phone the most that I configured myself. Mostly just fun to watch while driving on the dash mount. The load meter is just cool. Accelerate at all and it sweeps up like your taking off to the moon.