The US specs are that way because of the use of the Nema 5-15 outlets as you stated. The User Manual clearly states the exact input power requirements across all models. Both models use the same exact power supply, the only difference is the outlets. We have tested 240 Volt ~18 amp loads (space heater) being switched on and off at a 30 second interval for days at a time without issue, even on the US unit, because we figured someone would try and wanted to ensure it was safe, even though it is not recommended.
An SSR would be more ideal for rapid switching I agree but the constant switching on the mechanical relay doesn't make it unsafe, it will just reduce the life of the mechanical relay quicker.