I note this is an old thread (October), but just in case somebody reads threads this old...
I worked for many years with "cheap" inverters, particular back when 'modified sine wave' - just say square wave and drop the BS - inverters were just about it, and they were *expensive* (like $1k for 1kVA). Pure sine wave inverters of this power output and higher were so expensive your hair would turn grey (and now mine has!).
I sometimes used CVTs to fix the square wave output. Exceedingly inefficient. However, the output would drive things like audio power amps and stuff with virtually no audible noise. Feeding the square wave in resulted in a terrible buzz (not hum, no ground loops were involved). They were also the only solution when dealing with some mains operated equipment that uses a capacitive voltage dropper - a square wave would kill these in minutes, usually seconds, and sometimes cycles!
I played with CVTs from 100W to 2500W. The 2500 came from an inverter and was built as a UPS. The inverter was square wave, and the CVT gave it an almost perfect sine wave output. Losses were horrible, at no load the thing still drew significant current. At high (max) load it was in the order of 80% to 90% efficient. I did graphs showing how the output voltage coped with different loads, including overloads... the voltage collapses.
This was before SMPS were readily available, and especially for old colour TV sets, the CVT was virtually a necessity!
In the present, pure sine wave inverters are cheap ($200 for 1kVA), and nearly everything uses an internal SMPS design which can cope with square anyway (and many can cope with just straight DC - at 90+ volts).
Good CVT: Very clean output. Can 'replace' almost a full missing mains cycle. Almost indestructible.
Bad CVT: Extremely inefficient, and get very hot. Can not work with an overload (but will not be damaged).
Unless you are really on a budget, use a modern pure sine wave inverter (but beware, the 'cheap' ones do NOT live up to their surge ratings).
Cheers,
MM.