I can't say about fitting to an A500 but I have a similar design in my Seicento (roughly the same peak torque as a stock A500) and it is pretty brutal. Power delivery when it works is delightful (feeling a FWD car accelerate *and* pull you around a corner still makes me smile every time). The downside is I'm always waiting for it to grenade on me but five years on and it is still going strong.
In terms of testing you should find that the diff proportionally "locks" when power is applied and will relax to 50/50 under power but won't increase the split while under load. Putting power on and just turning in doesn't help with understeer on my car but putting power on after turning in does. Judicious lift-off on entry and possibly again mid-corner seems to get it doing exactly what I want and helps with setting the rear of the car up properly.
The only other point of reference I have is from an Integra Type-R I used to own - that would allow a flow of power regardless but the chassis was very, very different and less prone to understeer to start with. It still needed modulation of the throttle to get the LSD working though and the difference between on and off was nothing like as pronounced.