Well, I'll answer my own question. I bought ReelDirector (at 1.59€ I wasn't taking much of a risk) and it seems that for the purpose I had in mind, it's close to unusable. I haven't had much time to work with it though, and it looks like it's going to be a while before I have the bandwith and time to upgrade to iOS5, so I may keep trying. But so far my impression is rather bad.
My 10 minute video appears in the timeline as a 2 cm wide box, and I haven't found a way to zoom in, so precise placement is impossible. I can't preview the video in editing mode, much less preview the changes I make (I only want to add sound so I'm not touching the video itself). To check the effects of my changes, I need to render, and apparently the render reprocesses the whole video even if I only added a tiny bit of sound and did not change anything to the image part. And finally, if I cancel a render before it's finished, then start the render again without going to edit mode, the render starts again from the beginning.
So for the moment it looks like my 1.59 € were wasted. But as I said, I can't buy iMovie at the moment, so I may learn to use this app after all. Or maybe I'll just do the editing on my laptop, which is probably the only way to do it anyway.
