I got to use a wifi dongle from OBD Innovations, the vGate iCar 2. It's an ELM clone, like most of the others circulating around I guess. The vendor is very helpful though, and answers tech support questions quickly. They sell a bluetooth version as well (as noted, if you have non-jailbroken Apple gear you're stuck with either the $100 units (when available) or wifi. Similar problems with external GPS units as well. In any case this dongle is about the size of my OBD cover. Tiny. Has autooff, but I can't get it to automatically come back on, at least in my Ford. Works fine; just select it where you connect to wifi, and then fire up your app of choice. I've been using Dash Command, by Palmer. They certainly know their OBD stuff. They also sell a $10 set of Ford-specific PIDs that aren't included in regular OBD. I got at least a few of those free by customizing a Scan Gauge to read them (basically adding some hex strings), but these make it super easy. There are a lot; for me, the key one was with transmission temperature and some other stuff.
I like Dash Command, but like so many it's oriented more to the sports car or tuner audience. It does have a tilt meter for offroaders. You can customize skins, and gauges, but I don't like their looks much. I'd prefer to just have big numbers since I think I can tell RPM from oil pressure (be bad if I did mess that up....). They do have great tech support, and make a lot of other OBD products. I'd say an offroad-oriented OBD/GPS app would be quite popular; it would have more detailed trip meter stuff, make use of that tilt meter, do logging, speedo adjustment for bigger tires, and things like fuel calculation to destination. Depending on the sensors available, it might do some trick things with wheel spin, time spent in 4WD, automatic speedo adjustment when using the transfer case, etc. I may check out some other OBD apps; more seem to be coming on line. I noted that Rev hasn't been updated in like forever; not likely to invest in that. Anyone try any other iOS apps?
Rob