Availability 9":
The 9" are not that hard to find. I got three from auction sites here in the Netherlands in the past 2 months. The first one (that's in the cab) was $20, the IBM was $10. I bought one last week for $15 for a second project. I prefer pick up, because these things break easily. Check for burn, because they where also used for point of sale machines, etc. In vertical position they are perfect (as long as you play vertical games) on max. 800x600. Not all monitors can be stretched horizontally/vertically, so you get big black borders (check this before you buy).
Comfort:
When you put the cab on a table it's perfect to play while standing behind it, no problems. As you can see on my site, my son (6 yr) has found a good playing position too.
I think it looks pretty cool, but if you go for playing most mame games, including fighters, a table top with a bigger screen is better.
I will put more info on my site when i am done, it's just a wip-page now.