skip the expensive french mandolin (all metal) and go for a nice cheap japanese mandolin. The japanese one's are mostly plastic with simple removable (and SHARP) blades and attachments. They're much more portable and easier to store and only cost $30. The only real reason to go with the french version is if you're looking to do waffle cuts as the japanese mandolins don't come with that sort of blade.
If you don't have a really nice chef's knife then this would be the top necessity. The best way to choose is only loosely based on the type of blade it has. The most important thing in any knife is how it feels in your hand. Get them to bring you out some veggies to try chopping/slicing/dicing. You'll want one that's super comfortable in your hand and one where you feel you have a lot of control over it. Personally I think the new Henckel Profection knives are beautiful pieces of machinery.
"You can demonstrate the purpose and limits of human digestion with a simple experiment: eat a steak with some whole corn kernels, and see what comes out the other end. It won’t be the steak."