That Isotap's cord is falling apart!
I have a WP-25A too. The only problem with them is if someone switches the voltage while it is under a load - the contacts burn up easily. I use mine with a smallish (175VA) variac I built, so voltage change is made there, and I leave it on the 105V setting.
My other isolation transformer is two back-to-back 115V:48V/30A Control transformers I picked up at a DRMO auction in '88. Heavy? Suffice to say the transformers lay on a plywood dolly with casters. I plug my bench power strip (fused at 12A) into it and presto, isolated test equipment. Sets get plugged into my PR57 or one of my homemade variacs.
I have a rack mount Elgar power conditioner (an ex-NASA piece) that is isolated and removes RFI. NASA used it on a thermal contrlller for a laminating oven. I got in '06 from an eBay auction for 5 bucks, but had to pick it up some 35 miles away, as it weighs 80 pounds. I have yet to use it, beyond wiring up a power cord and installing it in a rack.
Cheers,