It's a metric used to compare different companies at different...

It's a metric used to compare different companies at different stages of development so of course it has its limitations but I wouldn't say it's terrible. It gives a rough indication, which may be useful where there's limited information available. Saying that, it'd be good to see a column for resource type, recoveries and other variables that are available etc. but that'd require more effort, something you can't expect of people to provide freely on a public forum.