The 0561 clip is one of the best I have ever used. I prefer it to the OG 550s any day. The cutout on the outside on my 0561 has never hung up on my pants or jeans or whatnot. I know its a real concern with some folders, but the rounded corners of the cut out help alleviate this problem completely while making the entirety of the lock bar more inline with the blade.
I prefer a deep-pocket clip and it's a bit amazing to watch something the size of my 561 disappear in my pocket.
That said, the clips on my 550 and 551 fit more securely in my pocket. The 561 moves about more in the pocket, although it's never fallen out.
Another point in favor of the 550/551 clip is that they are a bit flatter; I'm more aware of holding the 561 clip when I grip the handle.
Both clips are excellent -- just different.