I've ridden the TSDZ2 (the B version has some improvements but none related to most of what I'm about to say at least that I'm aware of) extensively on trails, including fairly technical trails, although mine is running the OSF at 52V but I do often use it as much lower power levels around 350W. With the OSF at least it's very responsive and easy to ride off road, the biggest issue is the limited RPM range and limited peak torque and that's with the 52V battery. With the lower voltage battery the issue will be worse.
The issue is that at low RPM the torque is limited due to the low current limit so you have to be in the right gear to let the motor spin up and provide good assistance but then since the max RPM is so low, lower than your max pedaling cadence probably and power tapers off before that point you run out of motor RPM so you have to shift accordingly. If you generally ride at a slow even pace like I sometimes do it's really not an issue but if you want to pick up some speed on flat sections and climb hills gear selection is a thing.
It's not a huge issue but considering now there are more options available on the market that are less limited, generally by having higher power ratings and many of those options potentially are more reliable considering the TSDZ2 has a not great track record. I would say I like my bike and am pretty happy with it from a pedal assist bike but probably wouldn't choose the TSDZ2 again over the newer offerings.
And what I mean about higher power drives being nicer to use in this way is you have to think of the peak wattage rating as only one part of the puzzle, what you really want is the ability for the motor to output a known amount of power or torque depending on how you want it to feel at a wide RPM range matching your cadence, which will often vary a lot more than when riding on road. So 350 watts may be plenty but if if only gives you that in a narrow RPM range and you get far less above and below that it feels awkward and you end up shifting a lot. While a motor that can provide 1500w peak but is limited to 350w in the settings will be able to provide that 350 much more of the time.
On the reliability point I've had no serious issues and many have had great results, however many have also had numerous failures and it seems that questionable QC means it's kind of a game of chance unfortunately. The one perhaps most serious issue is the axles snapping which will be at a higher risk when riding off road, I think so far my light weight has kept me safe but if you weigh more it's a concern. Perhaps the advantage the TSDZ2 (which the B version has made some improvements but only some) is the problems and solutions are well documented while some of the other options are too new for us to really know longer term their reliability, but they certianly seem better engineered than some of the frankly stupid shit in the TSDZ2 (circlip slot that makes the axles break, thermally isolated motor, sloppy axle spacing tolerances).