Had 2 customers do it here in NY/NJ and someone else in FL. Not mining related, just manufacturing

Saved them a lot.
BUT:

1) Everything is 'your fault' not the fault of the power company until you can prove otherwise when it comes to low power issues. 3 states, 3 different power companies, same BS.
2) If you do have issues they will not even test TO the transformer without your electrician being there.
3) If you do need parts / repair you can be down for a while. Unless you have a spare $50k transformer sitting around like the power company does.

For my customer that had a lot of issues it was stressful and annoying, but they could function on a limited bases.
A mining facility is going to be off....

-Dave