It's weird, I have a set of 9 speed ergos on a Shimano cassette on my road bike, and it's pretty much fine,
sometimes a bit jumpy in the big cogs, but I can live with it.
However, I had a cyclocross bike with the same set up and it was much worse - shifting was very inaccurate and
jumped quite a lot. The only reason I could put up with it was that I mostly rode round in the mud the lowest gears and didn't shift much
I presume it depends on how well you set up the indexing in the first place.
In short, in my experience, it sort of works but don't expect perfect accurate shifting all the time.