I've no objection to getting a better tool for that specific job. They're still electrical heating elements, so they're still using roughly 100 Watt for a typical car or truck engine.
Their main disadvantage is that they tend to have an electrical plug you have to fish out and connect at night, and put back safely in the morning. People tend to forget them and drive off with them connected, then rip the cord off. So what I've personally recommended to a few people is this.
The cord is bright orange, obvious sticking out from the hood, and 25 feet long, The hook on top is also very handy for storing it away safely when you take it out from under the hoood. it's very useful for seeing what you're doing from _under_ the car when working, as well, and if you have to you can still put a compact flourescent bulb in it. That didn't used to work well, but some of the flourescent bulbs are small enough now.
It's not a perfect solution, but it still works quite well.