I can't comment on the pure sine wave inverters. When I was in college I worked at Batteries Plus where we sold a fair share of inverters. We sold Triplite which I'd probably stay away from unless you're going high end. I've seen a fewr of their 100-200W units fail or they just start blowing fuses left and right. There's a reason why the cheapies are so inexpensive and its obviously cheap parts. Though the two I own are cheapies (got for free) and I haven't had any issues. I mainly have used them for long car trips and using my wife's beasty 5 year old P4 Toshiba laptop (it's heavy and now always power efficient). I have a P3 Kill-A-Watt meter and at peak 100% CPU usage the laptop uses about 100 watts.
Keep in mind what the specs for your usage of your inverter is. My wife and I both own Focus's which have an amp limit of 10A on the cigarette lighter. Volts x Amps = Watts. So on our cars 12V x 10A = 120 watts. With the 100 watts max on her laptops, I'm within that range. Most laptops don't use beyond 100W, especially new power efficient ones. So anything beyond 120 Watts on our cars would need an inverter hard wired directly to the battery of our car. Each vehicle is different though.
Cheapy inverters may say 360W max! But they only come with a cigarette lighter plug. Higher end units will have additional cabling for hard wiring for your vehicle or clamps to attach it to an external deep cycle battery - say a Marine Battery or Sealed Lead Acid battery. When using inverters off of batteries, make sure its a deep cycle battery because if you drain say an Auto battery (designed for starting) down too many times and too far, it will end up damaging and greatly shortening the life of your Auto battery. *See wife left car lights on 3 times in a week.
