<==== The Space Bar, upside down on a geared bike.
I was asked about an On One Mary Bar yesterday and it is a fantastic bar. (Do go to the link and read through Brant Richards excellent take on why these types of bars work so well.) The thing about the Mary, Midge, and Mungo is that while they are great bars, they cost a heck of a lot more and are not as easy to get a hold of as Origin 8's Gary and Space Bar. Quite simply, it's a matter of supply and economics for me. Otherwise much of what I will be writing here could be said of the Mary bar and it would be a great bar to own. Maybe someday......
<====You can use the Space Bar with your "regular" stem.
Some folks might be a bit concerned with positioning with a Space Bar. Not to worry! I have found that by overlaying a "standard" swept bar over a mounted Space Bar, that the actual end position for the hands is virtually the same. The difference being the angle that your hands are at. The angle of the grip section is close to 40 degrees and there is plenty of room for controls of your choice. The bars do have rise (or drop) and you can gain about an inch and a half of rise if you so desire. I have run the Space Bar upside down with excellent results as well.
<===The Space Bar plays quite well with Ergon grips and becomes even more useful with them, in my opinion.
Out riding, the Space Bar puts your elbows in a more relaxed, next to your body position and aligns your wrists and fore arms in a more natural way. My riding has shown me that they work just fine in single track and turning tight corners isn't a problem. I especially like the leverage I can generate out of the saddle on climbs. Imagine hoisting a pail full of water upwards with one hand and you might see how it is while out of the saddle pulling upwards on the Space Bar. The bar is plenty stiff, no noodle bar here! That means that if you run a rigid set up, the Space Bar may not be to your liking from a comfort standpoint. It doesn't yield to trail obstacles much at all!
I will give you my thoughts on the Mary bar in comparison here. (I think I can speak on this from my Midge Bar experience) The On One product is a much finer looking piece, no doubt. I would also suspect that it is slightly lighter than the Kalloy made Space Bar. The center section of the Mary is slightly different, most notably the clamp area, which looks much cleaner and neater than the Space Bar's does. Overall, it is a better looking, slightly lighter, and probably a slightly more comfortable bar than the Space Bar. However; you will pay nigh onto three times the price of a Space bar for a Mary Bar, so it comes at a premium.
In my mind, the Space Bar wins for it's versatility, toughness, and value. The average retail price for a Space Bar is about $25.00. Not bad for a handle bar and great for something that breaks from the normal 5-7 degree flat bars and riser bars that don't have more than 10 degrees sweep. You don't have to use a different stem, and you can use non-traditional grips, like Ergon grips. All your controls will work, no special considerations there either.