It's a pain compared to everything else, but to me they're worth it. After you've done one, it doesn't seem so bad. I like them because they don't get the burnt taste that cartos with filler get. I can't stand those, so I always drip. These are great for driving, or if you're going somewhere that dripping isn't practical. You have to use a syringe, which is a definite drawback. Makes you feel like a junkie.
Here's a video on how to do it. To me, the video made it seem harder than it is for some reason. I can fill one in about a minute.