I got my first Logitech product about a month ago (trackman Marble) and, while it's certainly an "OK" product, comparing it to Kensington's old Turbo Mouse or their new version, is like comparing day and night. I haven't had any need for support at this time so I can't offer anything there. I think that, with the comparison between the two, the Logitech product seems to designed for larger hands.
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Why the Slim Blade? Other than the large (and extremely comfortable large track ball) I've grown accustomed to Kensington's Turbo Mouse and it's new sibling, I've found that with the larger track ball, you need less side-to-side finger movement to move the cursor left-to-right than with the Logitec's smaller "marble" products.