I will qualify this quick review by admitting that I am a card carrying old fart & a gadget nut. My background includes a mechanical engineering degree from the 2nd third of the 20th Century, instrumentation R&D at NASA, and software development in my twilight years to make a comfortable living.
All testing was done on my '05 Jeep Liberty CRD which has had every single TSB and recall every published done to it - including F31 & F37. Part of my motivation for wanting more instrumentation on it is the seeming vulnerability to EGR related issues (Mine failed at 36k miles). That and I was curious to learn more about the infamous Off-Road-Mod and what actual affect that might have on engine operating parameters.
I started out modestly enough. Purchased a SGII for ~$150 and began to experiment. I did learn quickly that the ORM does indeed reduce the intake air temperature - SIGNIFICANTLY! Some 35-45 degrees F under my test conditions. That alone was comforting info.
But alas, the SGII kept locking up just when I'd want to be observing something interesting. I emailed Ron Delong (software guru at Linear Logic - the developer of the Scangauge II) and he tried some things to improve this situation, but so far the problem presists. It is an annoying more than fatal flaw. It just does not allow me to count on the Scangauge II functioning for an entire trip - unless the trip is relatively short (maybe 5-15 minutes or so). Your experience may vary...
Next I started thinking about this problem and decided that perhaps a different vendor's solution would behave somewhat better. Did some online searches and eventually settled on a DashDyno SPD unit. I sprung for the Pro edition as it included some fancy PC software that I've yet to find a use for - but it may come in handy yet. Don't tell my wife I now have TWO of these types of devices.

Maybe I will sell one of them after I learn all I can.
The DashDyno is functionally similar to the Scangauge II - but differs greatly in the user interface and the wider variety of gauge display options it offers. The DashDyno also has dynomometer capabilities that would have appealed to me more in my youth for that old TransAm I had... ahhh - but I'm digressing here...
To answer the basic question - yes, the DashDyno SPD also stops responding at intervals that are recognizably similar to the SGII. One big difference though is that the DashDyno SPD utilizes a 128MB "SD Card" as a solid state disk drive to hold setup parameters for gauge settings. This feature allows me to remove the SD Card and use my PC to change the data acquisition rates independently for each gauge parameter. Thus I can get turbo boost pressure (PSI) every 250 ms, and only ask for say, coolant temperature values every 5 or 10 seconds since they don't change very rapidly. This technique appears to significantly reduce the data traffic on the OBDII bus and the lockups seem a little less frequent and less annoying. But eventually it STILL locks up. No cure has been found. Both gauges require the engine to be shutdown for a minute or so and restarted before they will talk to the OBDII port again. Strange but true...
The SD Card can also be used to log information about the vehicle performance. This could prove very useful for someone trying to document the effects of performance mods, etc. It also can be used as a pass-through via USB cable to a notebook PC to further enhance the data collection and analysis capabilities. A few years back I'd have loved to have had this setup, but so much of it goes unused in my current needs that it is a bit of overkill.
Between these two options, the SGII is the more cost effect purchase. It costs less than half of what a DashDyno does. But then, the DashDyno has that dynomometer capabilty, data logging, etc., along with 0-60, 0-100, 1/8 mile and 1/4 mile timing, speed, horsepower and torque curve data acquisition that the SGII lacks. If you're really into gathering data and documenting performance parameters for analysis - the DashDyno is the more adaptable solution.
Now if only
someone on this list could tweak Chrysler/Jeep's Technical Support group and get them to
fix the stupid OBDII - ECM data communications failures I could be very happy with both of these devices in my toolbox.
I should also point out that the DashDyno SPD does provide a Fuel Rail Pressure parameter that displays the 5,000 to 22,000 psi of the fuel rail. Its certainly a rapidly changing value.
Neither gauge provides access to the Fuel Temperature Sensor on the fuel filter assy. I have not fully explored the xGauge feature of the Scangauge II - so it might be possible to query this temperature once we figure out how to ask the OBDII for it.
If you have any specific questions, I'd be happy to try to answer them.
PS - the xGauge capability is NOT duplcated by the DashDyno.
PSS - try as I might, I have yet to find a way to get either of these fine instruments to "automatically" turn off the MIL upon startup.
PSSS - Since the SGII has dual RJ45 ports and is rumored to allow you to daisy chain two such devices together, I'm currently building a suitable cable (the PINOUTS ARE DIFFERENT) so I can test using the two devices simultaneously. I'm not very hopeful here, but am game to give it a try.