Evaluating your OKRs is an essential element of implementing them. Rapid learning for your business and your team is a central aim.

Depending on the maturity of feedback culture of the company and the number of people to be involved (in best case everyone who is contributing to the OKRs), the most beneficial feedback method should be chosen and implemented as a regular, firmly established practice at least at every end of an OKR cycle.

Anne Weise, in 'Objectives and Key Results: Continuously improve on using the OKR method' on the Thoughtworks blog

As we said above, the of the essential traits of the Key Results you've selected is that they're easy to measure. That should mean: