As good as the results you get by hand, I got frustrated with the marks that you couldnt remove. The PC sorts this out - saying that, people are finding for serious paint correction even the PC wont cut it.
For a good shape car the PC is the ideal tool to take your finish a step further. Its not a cheap inital out lay, but seems well built so should last a few years, and its easy to recoupe the costs after a few paid details.
The main problem with other orbital sanders is getting backing plates and pads etc for them. I know a few guys use a Dewalt one which you can buy over here with good results.