Mine ? It's the Tacx Genius (actually genus Ironman which is the same, but a better price when I bought it) and although magnetic it makes a fair fist of adjusting the load vs speed. The incline simulation is 20% to -5 (yes it can power downhill, why?) Part of the reason I chose it was a reckoning that if it could simulate up to 20%, it would be better at the lower gradients/resistances. I was probably wrong.
As far as I can make out, the software sets the power and the device maintains your output, critical that is the bit where it calibrates, which is very odd indeed. To do it, you kick the pedal a fraction of a turn, the motor spins it up to about 20mph and then freewheels to zero. You then have to loosen or tighten the roller on the tyre.
In use, your cadence determines the absolute resistance so without changing gear you can either spin at 90 - 100+ or mash at 60 -70.Drop below about 50 and it all goes a bit pete tong as the resistance rises exponentially - stop with any target wattage over 100w, say, and it is virtually impossible to restart, only way to do it is to dial it manually then switch back to erg once you're spinning. Hopefully there will be a firmware patch to phase the resistance in over a fixed speed (8 mph?) but at the moment that's a severe drawback and one reason why the 20% gradient offered is probably not the best option.