I just completed a wet test. The setup was:
8 gallons of water circulating through my boil kettle (whirlpool). My March 815 pump was set to half throttle and I use 1/2" silicone lines. The IRIMS devices was a 12" tri-clover extension tube with 7 x 300 watt 120v band heaters.
This was not a simulation of my mash. The water volume was a couple of gallons more than my usual mash and I was using my boil kettle. Also, I didn't cover the kettle (my mash tun is covered during mashes). The IRIMS heater was not insulated.
I'm a bit disappointing in the results, but I don't think all hope is lost yet.
I ran two runs with the IRIMS and found that it could only maintain temperatures at 100%. My test runs were for 10 minutes each.
My existing HERMS device (An insulated 1 gallon cooler with a 2kW element and 1/2" copper coil submersed in the water) was able to raise the temperature of the entire mass of water by 4.3 F in 10 minutes.
I repeated each test twice.
I'm going to build an insulated box for the IRIMS device and see how much difference that makes. I would say my HERMS setup has a significant advantage since not much heat is lost to the atmosphere compared to the way I tested the IRIMS setup.
If I can get the same performance as my existing setup, I'll switch over just for the simpler and more compact setup.
But its looking like you will need more power than is available with 120v if you want to do any serious step mashes.