Ooh! I have a nice old Bron mandolin (nickel-plated brass w/stainless blades) with a straight blade, perpendicular to the cutting stroke, and it murders tomatoes. I also have a plastic Börner "V" slicer that slices tomatoes beautifully, uniformly and quickly.
My Zyliss has a V-blade that's adjustable by inserting different thickness panels. It makes quick work out of anything you throw at it. The only thing I dont like is the plastic frame and all the nooks and crannies underneath that you have to clean. The guard works great because it slides on a track. The thinnest you can slice is .75 mm.