Xentry PassThru is a subscription service that is offered by Daimler to Independent Service Providers to allow them to perform certain repairs of vehicles and control module programming. The US version is mandated by MBUSA rules, and the EU version is mandated by Daimler AG, so although they are both used by independent workshops, depending on if you live in the EU or US, they are priced differently and offer different features.
To clarify what PassThru software is, when OBD1 was common in the 1980s and early 1990s, each manufacturer had a different connector, diagnostic machine/computer, used different protocols and provided unique trouble codes depending on the make of the vehicle. The J2534 initiative attempted to standardize that, creating a standard set of Powertrain DTCs and other diagnostic information in the OBD2 standard (and the EOBD standard I assume is similar in the EU, but I am honestly not familiar with it). J2534 also provides an avenue for independent workshops to program, flash, and code control units using a standardized protocol, connection, and VCI for many makes and models. J2534 is not as comprehensive as the automaker’s own diagnostic tools, but provides a level not seen before available to independent workshops.
Instead of purchasing an SDConnect, Xentry Kit, or other automakers proprietary diagnostic device, J2534 allows you to purchase a J2534 compliant VCI from a number of manufacturers such as Bosch, Snap-On, AVDI, Drew Technologies, etc. Once you have one of these J2534 adapters, you can use it with the automakers software to communicate, troubleshoot, flash, and code control units not only by Daimler, but by Ford, General Motors, Dodge/Chrysler, etc. They all have different software that you must use unique to their make, but use the same interface to connect to the car, and has the advantage of being installed on a non-proprietary laptop, such as a standard Windows-based ThinkPad or Surface Pro.
In summary, the PassThru option is less expensive, less capable, but more flexible and is certainly better than the offerings just 7-8 years ago. You may order the Xentry PassThru subscription from Daimler and install it on your laptop and it is licensed to you, however in the US it will *only* communicate with control units that are emissions related such as the ECU, SCR, etc. This if course is dictated by the permissions the StartKey allows, and the StartKey you are assigned with this subscriptions is artificially limited to those control modules with the exception of 2018 and newer vehicles, in which all control units may be interrogated and flashed.
If you want and need full dealer capability (legally), be prepared to spend $$$ in the US shop http://www.chinacardiags.com/wholesale/jdiag-elite-ii-pro-j2534-device-with-full-adapters-41883.html . It will flash, code, and program all control units in the vehicle.
I hope this clarifies it.