What are the opinions on engine cleaners?

If I was to purchase a car that has had the same oil in for 10 years and the oil is filthy, would these engine cleaners:

1/ Do anything?

2/ Would they damage anything?

I see some recommend running the car for no more than 15 minutes with the cleaners in.

Would you use them in a modern car such as an alloy V8?

Just curious, thanks.