...One final observation that I made (using the device like the Slapchop) was that I had to get out a knife and cutting board ANYWAY just to get many of the vegetables prepped (cut off non-edible parts) and trimmed to fit under the round plastic "hood" that contains the cutting blades. By the time you cut them into ~2" pieces, making a few more cuts with a knife didn't take much longer.
This is what I've always thought about these things -- if you have to cut things up partway anyway, it kind of loses its value. And I'm always one for more convenience -- I buy only bagged salad greens, etc. This just seemed like more work than it really saves.