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I played one when they first came out. I was very impressed. Has a great sound and very good tuning. Easy low end, decent high register for a big horn. If you can play lightly enough for a small ensemble with it, you could use it as an all-around axe.

Honestly, I don't recall the Ab exactly. I know that overall the tuning was excellent. Definitely worth your time to take a test drive on one.

It's worth playing, but not buying sight unseen (er...sound unplayed?). I tried one once, and it was okay, but not at the top of my personal list.

Honestly if your only restrictions are 5/4 and under $20,000, that doesn't narrow your options much.