Is there a way to show index_advantage more friendly?
As Michael Green noted, this doesn't trivially convert into a percentage. This query looks at the top 25 "scores", based on this formula; but those scores aren't based some known maximum.

If you looked at all the scores, they'd be based on query activity where SQL Server thinks an index that might help, not all SQL activity. And, of course, the numbers are much lower when you're server's been up for 1 day vs. 1 month.

Ultimately, I believe these scores are intended to give you a basis for comparison; a query scoring 2000000 is more likely worthwhile to look at than one scoring 200. - RDFozz