99% of "circuitry modelling" is promotional snake oil for a company to sex-up their conventional DSP plug-ins. It's easy to tell this isn't the case here, as this is one of the best tube simulations I've ever tried.
The proper circuit model brings my machine to a screeching halt, but the hybrid model is still very good - often I'll produce under hybrid, and then render under the model. This is an addictive "mojo" plug-in. Few others compare.