I've had a TrailDash for a while now too. I wrote a review of it on Amazon.com not too long after I got it but I'd say I feel about the same about it now.
If you have a manual, the TrailDash apparently has problems detecting that you're in reverse to auto-switch to an attached reverse camera. (I have an automatic so that wasn't an issue for me.)
I'm pretty certain it's just getting its data from standard OBD-II requests.
I know one of the parameters I set mine up to display for me is the transmission oil temperature, but that's apparently only an estimated value. (If you put the Jeep in Park, it immediately shows a temperature of 0.)
I also have mine displaying the fuel level as a percentage, and I've noticed that seems to be off a bit. If I fill the tank, even trying to top it off to ensure it's as full as it can ever get? The TrailDash will report it as 95% full.
I run with their "87 octane performance tune" - but I'm not really sure if I can tell any difference between it and the stock tune. (In my case, I switched to it when my Jeep only had 1,000 miles or so on the odometer ... and then I found out these engines are known to "loosen up" or electronically release some sort of artificial governor on the engine at around the 1,500 mile mark. So that really threw off any ability I might have had to give a "seat of the pants" estimate of what it did or didn't do for me.)
Honestly, I'm just using their tune right now because I paid for the TD and their "custom tunes", so I want to at least use what I purchased. (If it's like MANY vehicles on the road today, I'm sure there's at least some excess richness in the air/fuel maps it dials back, meaning a potential small savings in gas usage.)
All in all, I wish the price of the TD was a little lower. If you could buy one for $250-325 or so, it would be a "must have" purchase for your Jeep. At more like $500, it's more questionable. I've been a fan of custom tunes for other cars I've owned where they made very noticeable differences, so I jumped at the chance to do the same on the Wrangler. But eh.... this one's unremarkable in that area. It's nice having it mounted with their "dashpod" to my center console and using it as my backup camera plus extra gauges. But it's more of a fun tech toy than a necessity.