Ok, so presumably sufficient for less demanding stereo applications as long as both transmitters maintain wireless connectivity to the receiver, based on your report using the similar Movo version. Certainly good enough for it's intended use for non stereo stuff such as dialog.
Most demanding usage case is going to be a coincident or near-spaced stereo pair, or a soundboard feed split across two independent transmitter/recorder units. First thing likely to be noticed as sync begins to drift is an image shift over to one side, possibly followed by a very slow phase/flange effect (although I think any drift would likely be too slow to hear it as active flanging), before the drift grows significant enough to begin to be perceived as audible delay.
A couple excerpts from the guide breakonthru posted a link to above which hint at what may be expected-
"Note: Using the jam sync method can result in very minor fluctuations in the synchronization between your devices over time (referred to as ‘drift’) as their internal generators aren’t perfectly matched. As such, we recommend performing a jam sync about every four (4) hours, or whenever you power cycle your cameras, to ensure frame-accurate syncing."
-and-
"A Note on Timecode Limitations
Cameras and other recording devices differ in how they handle internal video and audio file synchronization, as well as in how they accept timecode, and this can have some consequences for timecode syncing.
While the Wireless PRO system is perfectly synchronised internally between the receiver and transmitters, there’s a small chance that your video and audio may be out of sync by a tiny amount depending on a wide range of variables in the other equipment you’re using (this disparity could measure 1 or 2 frames in extreme cases).
Even with this in mind, it is still significantly quicker to use timecode to synchronize your files and then adjust them by a frame or two. We recommend you record a clap that’s visible and audible on all of your video and audio recording equipment. Once you’ve synchronized your files using timecode, this can be used as a reference point for nudging your video or audio if it’s needed."
One frame is ~30ms, two ~60ms,which represents a rather significant delay over the course of 4 hours in the worst case scenario. The last paragraph essentially describes how tapers have always gone about sync'ing two separate sources using a snare hit, clap, or verbal announcement.