I have multiple good news about this project.

RTL-SDR v4 SUPPORT
Our forum member, @danny325is, added support for RTL-SDR some weeks ago, and is now merged with the rest of the improvements. As RTL-SDR v4 is an inexpensive, ~$40 device, the barrier of entry was lowered significantly. For purchasing options, see their official site, there are multiple options (Amazon/Ebay/AliExpress). Make sure you buy the v4 version, as the decoder was not tested with earlier versions (I just ordered an older one, weeks to arrive).

WINDOWS BUILD
The project is built for Windows semi-automatically, meaning you can download a .zip, containing the whole project (no installer is needed). You no longer have to install python to use the core integrations, as the zround and p3 bridges are compiled to their own .exe files (each of such file contain the whole python runtime and dependencies, hence the 10 MB+ filesize). As such, once you have the SDR drivers installed:
1. plug in the radio to an USB port
2. double-click on openstint_hackrf.exe or openstint_rtlsdr.exe (and ignore the "untrusted code" warnings - it's not signed, hence the error)
3. double-click on bridge-zround.exe
4. start your ZRound, and set 127.0.0.1 as decoder ip address
You might have to allow the firewall exceptions meanwhile.

INCREASED RECEPTION QUALITY
Firstly, the symbol synchronizer was fixed. Previously about 8-10% of all frames were dropped. With the fixed version, I was able to lower the preamble-detection threshold while still maintaining a very high detection ratio. Long story short, we can detect and decode weaker signals more reliably now.

Secondly, a feature called "adaptive equalisation" was added. For super-nerds only: the transmit coils, the antenna and the whole transmit-receive chain has non-idealities, resulting in bit errors. An adaptive equaliser learns these errors and corrects for them. A few cars have to pass, and the system tunes itself.

The result of these two improvements, more frames are decoded even in non-ideal radio environments. In ideal ones, EVM figures lower that 0.05 are often observable (rssi > -10 dB; hackrf one).

RELIABLE PASSING TIME DETECTION
The "point of passing" was determined previously as "point of highest signal strength". Now there is a more sophisticated algorithm implemented.

I placed two transponders ~15 mm distance from each other. The new algorithm is reliably able to distinguish if the car passes the loop forward or reverse, based on which transponder passes first (tested at low speeds).

EDIT: the p3-bridge feature was removed; contact in private message if you really need it.