Generally the better quality the inverter is, the better quality sine wave form the output is. Inverters work by converting DC wave voltage into AV modified sine wave voltage, and then tranforming it up to the require voltage. Basically it uses electronic components to try and emulate an AC sine wave, which will never be a perfect sinewave, but will vary in quality compared (generally) to the price of the unit. Some equipment may not perform well if the sinewave is not of a good representation of an actual AC sine wave.
Same as anything really, you get what you pay for. If you're only using it for small loads like chargers & lights then pretty much anything will do the job, just make sure it's got the right australian standards approvals.