We've had an AP2 vehicle since March 2017. The early AutoSteer software was pretty bad - ping-ponging from side-to-side in lanes and making abrupt lane changes. Over time, AutoSteer has improved, and under normal driving conditions with clear lane markings, it now works pretty well, at least most of the time.
Based on the progress over the past year, AutoSteer has improved, lane changes are smoother, and it's able to better track lane lines, in more situations.
However...
This is still "beta" software - and we treat it as an experienced student driver, still trying to learn how to drive - and are ready to take over operations at any time, because we don't yet trust the software 100% - especially to react to unusual circumstances (such as construction zones with inconsistent road markings or tight lanes).
If you're planning to keep your Tesla for 4-8 years (or 75-100K miles), during that time, Tesla will continue improving the software, and based on the rate of improvement over the last 12 months, we're comfortable with what we spent on activating EAP on our 2017 S and 2018 X.