Most of the other square wave UPS make a lot of buzzing noise and make sounds ( relay switching sounds) during operatoin. But the interesting fact here is that it doesn’t make any of those hazzels and runs smoothly. Of course 900EB is a very small capacity for running air conditioning and refrigeration systems, but it depends on the heart and strength of the battery. Square wave is a bit awkward as many today use sine wave UPS systems. It was a bang for buck back in days.
It also has a relay switching lag for around 100ms.( 0.1 second time to switch on power supply after power is gone is not a big matter unless you have a power hungry desktop sitting on your table).