I am using Su-Kam 350VA/450 VA model(low frequency charger type) inverter from the past 20 years . Performance is excellent even after continuous use of 20 yrs. No repairs till now.
Battery charging is excellent. It switches on to trickle charge mode after battery is fully charged. All indicators like charging, charged, overload etc work well. Built quality is very good.
Normal battery of AMCO Cheetah make(flat plate) lasts about 3 years. I hope Su-Kam is still maintaining the same quality.
Since, it is based on old technology and output is sq. wave, a humming noise is expected. My experience with Su-Kam was very good.