@Woosh Thanks for your comment its very much appreciated.
I come from a model helicopter background and have been using Li-Po batteries for many years and I understand it that 3.7v a cell is the minimum volts before you start damaging the battery, so i try(not always successfully) to keep between 4.2v and 3.7v which, as you explained is within the 5 bar range, after Li-Po's pass 3.7v they do drop rapidly and at 3.5v they are basically useless. Also at 3.5v(if you go there regular) and under, they overheat and start to puff.
So in the interest of safety i work on the principal that 3.7v is the lowest i go with LI-Po, and that is where my low volt alarm is set, so the TSDZ2 display is working as it should BUT the bar type indicator definition is far too coarse when using Li-Po's. I have no experience of Lithium ion or LifePo4 (which most people use) mainly because of cost, so maybe it would be a more useful in their case.
As you can probably tell, i am a tinkerer (not Tinker) so the Bafang brand with its ease of adjustability and voltage readout suits me better, saying that, the Tongsheng TSDZ2 has proved reliable and is more economical with the battery, and up to 25% more mileage with the same battery setup. If i could find a small voltmeter system(cycle analyst is too big) and a narrow wide chainring system i would be a happy bunny.
So going back to the original question of Bafang vs TSDZ2 i would still say Bafang because spares and accessories are easier to find and it has a larger knowledge base and adjustments and settings are more accessible.
BUT i dont think you can go wrong with either.