I haven't been around for a while James, but this is a question worth answering. To start with, since the thread is actually about legality, yes what you are asking about (clearly a barrel bushing replacement comp) is perfectly legal; though a threaded comp (and therefore one that actually does something) would be legal as well. The pistol section of the AWB counts a threaded barrel as one regulated feature, but it takes two to make it illegal.
So.. about comps in general. Firstly, there are different types of compensators used on 1911s. You've got your barrel bushing replacement comps, your extended and threaded barrel (still using a barrel bushing) comp, and then you've got your threaded cone style comp. And as a side note a slightly different setup for bull barrels.
Now, I'm sure there are those that will say otherwise, but frankly those people are wrong. The type of comp you are referring to does a whole lot of nothing. There just isn't any significant baffle and gas redirection. The physics just aren't there. The breach of the comp has to be big enough to clear the barrel at tilt, so right there you've got a big problem with the whole point of the thing. That coupled with the fact that most bushing comps don't have multiple chambers.. makes them good at looking cool, and costing money, and that's about it. Why does anyone think they work ? Good question, the answer is generally that there is some perceived reduction in recoil because of the added forward weight. So, the heavier a bushing comp is, the more you'll think it's doing something. However, the added weight on the slide is also a liability. The more weight you add to the slide, the slower your cycling becomes and you'd need a lighter recoil spring to account for it using the same loads. It could also be argued that the added weight on the slide could batter the internals more without just the right balance of spring vs loads. Anyway, lets just put it this way , you will NEVER see a bushing comp on any real competition gun set up by a professional.
High quality threaded comps make a world of difference though. You really have to know exactly what you want them for though. Some comps will work better with certain loads, and some might require slide lightening work to be used properly with the intended load. So on and so forth.