We purchased one of these a couple years ago: http://www.globeslicers.com
I started a thread on the site asking about it some time ago... looking for it... here it is
. I'm not sure if it will help or not.
The Globe works like a champ. I've had to replace the grid attachment a couple times (and they are pricey), but we have definitely get our money's worth out of them before they start to degrade (razor thin metal grid... it's sharp!). The slicer blade for the grid has had to visit the bench grinder a few times too. Either there are rocks in our potatoes or soft metal is soft.;)
We use the grid to cut 3/8 inch cubed potatoes and onions for chowder and other soups and cut 3/8 inch tomatoes and onions for salsa.
We also use a julienne blade on carrots for our salads.
There are other applications too, I just can't think of them right now, but those are the main uses.
If you need a work horse for a high volume restaurant (and have a few grand to blow), I suggest the Globe. They even came by and gave me a demo AFTER I had purchased the machine. Call them; tell them you want to see it in action. There's a "request a vegetable cutter demonstration" link on that page in my first link.
Foodpump is right, too. Mixer attachments are great, and we employ them for grating cheese and a few things. I haven't tried their dicing attachments, though.
Anyhow, let me wrap it up here with a disclaimer stating that I am far from an expert on this subject, I just wanted to say that I use this product and am more than happy with it and so are the prep cooks. The others you suggested look like they could become clogged easily, leading to frustration and mushed vegetables. I wouldn't waste my money on them (not speaking from experienced use with them).