If it doesn't do the 15K resolutions, then how is it any better/different than a regular computer monitor?
Good question...1: It is an open frame monitor so it is easy to mount, especially for cocktail setup. Not having to modify the cabinet for a computer monitor was a benifit demon-seed was looking for.
2: Its tube has the same curve to it that any other arcade monitor (or tv) would have. This means that the 19" plastic bezels will fit it nicely giving the cab a nice clean appearance. Computer monitors have FST which stand for something like Flat Square Tube. Even the non-flat-screen computer monitors are a lot flatter than an arcade or tv tube. Having the correct tube adds some authenticity in my opinion.
3: The u3100 tube does not have a real fine dot pitch like computer monitors do. Its dot pitch is the same as a regular arcade tube. This means you will get a more authentic looking display than you would on a computer monitor. That is why some people use scanlines in mame on their computer monitors. Its hard to remember sometimes if you haven't played an actual arcade game in a while, but you can actually see the individual pixels without looking too hard. On a computer monitor everything is really smooth (too smooth for arcade games in some peoples opinion) You have to look real hard and real close to make out the pixels.
4: A 19" arcade monitor (u3100 included) means 19" viewable area. A 19" computer monitor has an 18" viewable area. (Suppose you could just buy a larger computer monitor to make up for this though)
If none of this or at least not much of it matters to you, then a pc monitor would do fine.