I have one.
It’s generally good. Though it’s crapped out on me a bit lately – might be a bit knackered. I got mine from Rose, which will be a pain if I have to send it back.
When it’s working, it’s ace. I use it with TrainerRoad, so I don’t think the gradient thing is very relevant – it’ll go up to several hundred watts, so that’s enough for me. One thing that I think is not as good as posher ones is that I do have to change gear quite a bit to keep it in its optimal range for controlling the power.
Personally I wouldn’t bother with any Tacx software – reputation isn’t great. Suunto ANT+ USB jobber plus TrainerRoad or Zwift and you’re good to go. I’d buy from a UK source though if I were doing it again…