The downside of OKRs is that it incentivizes everyone to sandbag their efforts and then stick to that effort. Also no one is going to stick their neck out on goals which are ambiguous or lack clarity. There is just no incentive - in fact there's a massive dis-incentive.

If you have a startup with less than 300 people and you have good communication and goal setting, don't use OKRs. Use KPIs and then nehlp your teams to keep iterating.

Input management is so much more effective than output management but it needs visionary leadership. Read: High Output Management - Andrew S Grove (ex Intel CEO).