I did test it  and it appears to cost 1.5%  in power. About 25 watts at high speed.

 also took it apart to figure if it really is 5000 va and 22.7 amps constant run.

I estimate it will do 1 unit at 1550 watts 24/7/365  with zero issues.
I don't think it can do 2 units at 3100 watts. 24/7/365
I think  the torrid transformer will get too hot.
I also think the power cord is  14 gauge  not 12 gauge.
So  for 1 unit in a garage it is okay it should protect the gear and last  but it won't last doing the 2 units it is rated for.

It is now on sale on ebay

https://www.ebay.com/itm/Norstar-5000-Watt-Step-UP-and-Down-Voltatge-Regulator-Transformer-Converter/332955089461?

I bid 180 offer he took it.
and ebay is giving ebucks 10%  so 180 -18 = 162  and my paypal gives 2 % so 162 -3 = 159

for 159  it will give me some piece of mind.  but  if you have  10 or 20   s15's this costs too much.