I don't but my friend does and I rode him a bit. She rode him barrel racing he was amazing and kind, sweetest horse. He's very responsive, and willing. Fast haha, amazing trail horse, great all around. She's owned him for 7 years now I think...
One of my mares, Nikki, is an TB/QH appendix. She's an amazing girl. Nikki will be 12 this year and I've had her a little over 2 years...Absolutely love her, she's my "go-to" barrel horse and I can always count on her to work for me. There are a lot more pics in my "barn", this is just one of my favorites.
I've worked with multiple appendix quarter horses but do not own one. The ones I work with now are off the track racers that are being retrained in barrels and poles.
There are a ton of breeds out there. Keep your options open for other breeds too. You might pass up the perfect _____ horse because your so focused on an appendix. They are nice horses but there are soooo many horses out there. Try lots and lots of them out! The right horse will present himself/herself to you in time.