I've had them for a while, but haven't used them on a machine yet. Just test run them on the bench. I have two air cooled 2.2Kw, that were $200 each.
Hundreds, if not thousands of people have been using these spindles for years (mostly water cooled, but more air cooled recently). If you set up the VFD properly, they are pretty good spindles, for the money. It seems that most issues that people have are due to incorrect VFD settings. These spindles aren't very tolerant of incorrect settings.