Redeemed a Turkish award to travel on UA from mainland to Hawaii. I had a schedule change and needed to rebook, and it was a complete nightmare. At the last minute (with 24 hours of travel), a UA supervisor at reservations was able to get control over the ticket and make the necessary changes. Previously, both I and UA agents made more than a dozen phone calls to TK with no success. Previously, one UA agent was actually able to get Turkish to reissue the ticket, but they reissued it for a UA flight that didn't exist. And then we could get no one at Turkish to do anything else to try to fix this problem.

I will say that if you have a TK problem, you MIGHT improve your odds by filing a "feedback" request with TK on their website which at least gets you telephone access to a different desk that might possibly think of helping you. They didn't actually help me, but it seemed more possible that they might.

I booked this ticket on TK because it was a crazy award deal, and I might do it again if it saved me more than half the cost of booking elsewhere. But, in general, I would avoid booking partner award travel on TK if you have any other plausible option. Just not worth the many hours of hassle. It's really unimaginable to me how they can be so bad at basic customer service.