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A lot of contemporary usability evaluation relies on easily measurable and readily available metrics like conversion rates, task success rates, and time on task, even though it’s questionable how well these are suited for reliably capturing a concept as complex as usability in its entirety.
The same holds for user experience. When an instrument is used to measure usability, e.g., in controlled user studies or via live intercepts, it’s often the simple single ease question, which is generally not a bad choice, but has its limits.
Note: For more information on usability evaluation, you can check the article “Current Practice in Measuring Usability: Challenges to Usability Studies and Research” by Kasper Hornbæk and “Growth Marketing Considered Harmful” by Maximilian Speicher.