I had purchased a 400w inverter from Sam's Club 3 years ago. It lasted until just a few months ago- an impressive service record for a $35 inverter.
Fast forward to last week-
My new 1200w inverter arrived in the mail. Like I do with all my new gadgets, I took it apart and examined the components. Everything inside is top-quality, and the biggest perk for me was the new fan design- much better, quieter and longer lasting than the 400w unit's fan.
I hooked it up in my truck and plugged in all my computer equipment and tools. Unlike the 400w inverter, this unit has relatively low line noise. There is still a buzz to be heard over ungrounded audio components but it is leaps and bounds better than the previous model.
I haven't had a chance to use the unit with more than 500w load, but so far it runs very cool and quiet- and efficiently. So far I'm estimating that efficiency is about 70% (watts out/watts in).