From the client's point of view, paying by the hour is bad news - and as a former client myself, I would never have hired a writer on this basis. Why?
Well, how long is your writer going to take? If they know before they have even started I would question their working methods. Some projects, superficially similar, take longer to write than others - how does your writer know which is which? So you're getting into an open-ended commitment to pay the final bill. Or are you? A few clients have asked me to work on an hourly rate but then say, "It's four hours' work." Now, how do they know? What they're doing is setting the fee for you.
From the copywriter's point of view, charging by the hour seems at first sight to be good news. After all, you get paid for all the time you put in. But consider this...
If you do repeated projects for the same client, I would expect you to get faster. It's called increasing your productivity. Let's say you're twice as fast. You're honest, so you're going to charge them half what you used to. Er, OK. So now you're a better writer than you used to be and you're charging half as much for the same job.
Charge by the project on the other hand and your client still pays the same amount for the same project. But now THEY get a better piece of copy and a fixed fee they can budget for, and YOU get an effectively higher rate for the job. Just be sure your writing IS better than it used to be! Of course you can come unstuck if a project takes longer than you thought it would ... but hey, them's the breaks.
