My experience as a performance management vendor:

- For very small startups: just talk. A lot, every week at least. Setting metrics is hard until you gain more visibility. If you can though, do it.

- For midsize startups: set goals with clear metrics/achievements (we use OKRs), and still talk a lot (one-on-ones and amongst the team). Metrics are here to set expectations not to be your final rating. If your manager wants to screw you, they'll do it with any system.

- For larger companies: Do as above + add formal appraisals. The appraisal is more about career direction.

This tends to work well because employees find it fair and predictable. And as others mentioned, don't wait 6 months to give feedback. A review shouldn't come as a surprise.