sp_BlitzIndex performance concerns in production
When you run it on a restored instance, you won't get any data about which indexes are getting used, and which indexes SQL Server wishes it would have had.

So it's not really all that useful - however, it IS useful to understand how long sp_BlitzIndex will take to run. If you're worried about performance impacts, you can run it against a restored instance on similar hardware, and that'll tell you about the performance impact - but just don't take any actions based on the output.