Hi MarkReb,
I know this is an older post but I figured I'd offer my thoughts on the topic.
The issues that have been observed on MR29+ with client balancing are because we updated to an active client balancing method that can be more aggressive and cause some client instability. These issues are much more prevalent in high-density wireless deployments with lots of clients and APs. I have not come across too many issues with band steering on MR29+. Generally, I advise having band steering enabled and client balancing disabled.
Depending on the needs of your wireless deployment and the combination of RF settings used, you could update to MR29 or 30 without issue.
For any potential issues that are observed after an update, it would be best to work with support if possible to confirm if there is a specific known issue we are hitting and get your case attached for tracking and updates on that issue.