An agile principle is to deliver a working product. Therefore, if you still need to measure something, it should be about the product and its delivery:
- Lead time – how long does it take to deliver the idea?
- Cycle time – how long does it take to implement the idea from the moment of the start of development?
- Sprint burndown chart – How much work is remaining in the sprint?
- Release burndown chart – how much work is remaining in the release cycle?
- Cumulative flow chart – what is the throughput of the team?
- Value chart – do we add value to our product?
- Complexity chart – do we estimate correctly?
Of course feel free to measure anything else. Like Customers satisfaction (Net Promoter Score), employees satisfaction, quality of development, quality of service, number of defects, support cases, etc.
In agile you should measure blockers, ideas implementer, experiments started and finished, the learning, etc. Companies, where requirements are too vague, used to measure even readiness over time.
Think about how to measure your goals and removal of your problems. Because these are important. And what about the measurement of people performance? Well, transparency and often retrospectives solve that without the necessity of further metrics.