It takes ages (days to weeks) to discharge through the small resistor and TL431, so you need to leave it mounted. Then there's the risk you forget it connected, and because the quiescent current is fairly high with that resistor divider in there, there's a risk of destroying the battery by overdischarge during storage.
Days to weeks ?

Lets make a rough calculation (assuming 100% efficiency and constant voltage battery).
A 2000mAh cell, at 100% capacity holds an energy of 4.2V * 2A * 60 minutes * 60 seconds = 30.24kJ
To discharge it to 60% of capacity you have to take away 40% of energy, that is 30.24kJ * 0.4 = 12.096kJ.
A TL431 withstands 100mA of current. Lets make it 80mA of average current (I didn't care much of that in the circuit I previously attached), now that means that at 4.2V and 80mA the needed time would be : 12.096e3 / (4.2*80e-3) = 36e3 seconds, that is 10 hours.
So unless I made some coarse mistake and unless you want to discharge the battery pack of an electric SUV I think it would take quite less than days or weeks.

The schematic I posted was just a quick guess of that in the photo. I do not know if they use a dedicated chip or if that is just the usual careless design with a generic shunt regulator.
In any case, with just few more components, it is easy to design a few µA leakage circuit (around 1µA in LTspice). It would cost no more than 1-2 euros/USD and might be a good DIY project.


notes:
- all resistor values should be changed according to the number of cells and the type of LED, do not forget about the maximum MOSFET gate voltage: a voltage divider or zener is needed in case of more than 4 cells.
- I just chose the first low Vth MOSFET model in LTspice, I've no idea about the price and other features, but there are plenty of suitable MOSFETs
- C2 is there to start the circuit. It might cause TL431 instability (oscillations) and would require a discharge button, so it might be better to just replace it by a (momentary ON) push button
with a series resistor (or better just use a bit overrated power resistor for R3)
- do not forget to take into account TL431 and resistor tolerances.
BTW - AFAIK - Li-ion batteries are not affected by the Ni-Cd memory effect and last longer if the discharge current is in the order of several tenths of mA rather than A