Shockingly bad interface. It's pretty comical - If you click any of the progress indicators in the queue before downloading the indicator fills to where you click it! Poor use of icons and bad layout too (for instance, two similar "reload" type icons - Bad idea). That said, it's currently downloading the whole series of Spiral without any bother, so despite the interface it seems to be working fine.
It shows promise, so I really hope that the author continues work on it to make it more user-friendly and polished. There are some useful options in the Preferences section too. Alternatives like iPlayer Grabber and iPlayer Downloader are far more together in terms of their interfaces, but suffer the opposite issue in that very often they stop working after a while (BBC Website changes?) or only download some programmes. Ultimately, that's no use, so this app could well be the one I stick with.
I'm assuming that due to the version, this is a very early release, and considered in that light the interface issues aren't a big deal.