I know that onlays are just half a crowns but are there any huge risk in them vs a crown?

More conservative. Less of the tooth is removed and the biting surface is covered and protected without going below the gumline all the way around the tooth. They are my preference for treatment whenever possible.
Onlay. Is a conservative approach to preserve the remaining sound structure of a tooth. If onlay fails later on, that's the time to have a full crown. The less tooth structure is left, the less integrity it has.