I haven't tried many swirl removal products (still trying to finish my bottle of 105), but so far it's been the 105/205 combo. 205 isn't really a replacement or newer model for 105, it's to finish it off. After using 105 you will likely have micro-marring. If you look in my 2nd detail thread I think I mention it and show a pic. It's like very very small swirl marks. The 205 is used after 105 to get rid of those.
I think if you wanted to use just one product, I think 205 by itself would do great. It would definitely take a little more work than using 105, but you wouldn't have to worry about following up with a finisher. I believe it has a 4/10 cut on the abrasiveness scale, as compared to 105s 10/10.
I couldn't imagine applying it by hand. Can't comment on it, either, because I'm never going to try.
