I wasn't criticising the use of an isolation transformer, just pointing out that if mains hum has already got into the signal path, fitting a transformer downstream of the signal is not going to stop it.
If however the mains hum is due to an earth loop, and it is not possible or convenient to fit earth lift resistors, then a 1:1 transformer placed in the signal pathway is a neat way to break the loop. But in adding an extra component into the signal path, the quality of the isolation transformer is important in respect of both frequency and phase bandwidth.
I note the transformer unit is fitted with XLR connectors. I would have thought if using fully balanced interconnects between items having true dual-differential input/outputs, mains hum breakthrough would not be a problem.