We installed the «PROsine 1800i Part # 806-1884 24V Hardwire w/ transfer relay», with «Remote Interface Panel Part # 808-1800» similar to what the Amel factory installed on Bill Rouse's boat.
Whether on or off, it makes no difference to RF noise levels on any equipment on the boat that I've noticed. Ours has worked fine and sometimes pretty hard for 4 years... in fact back in the States we used it as 24x7 power supply when on shore power given the fact all appliances onboard (down to the toothbrushes) are 230V/50Hz.
The only downside to this inverter is that it consumes somewhere between 25w and 50w just by being turned on. I have heard that more modern inverters are more efficient when on but not actually supplying any power... evidently this inverter design is at least 15 years old.
SM2K No. 350 (2002)