How does the Smeg TSF03 differ from the two-slot Smeg toaster?

It has four slots in two independently controlled pairs, so two people can use different browning settings at once. The two-slot model has a single set of controls and a smaller footprint.

Does it fit thick-cut bread?

The slots are on the narrow side. Standard sandwich bread fits fine, but thick-cut, fresh or hand-cut loaves may need trimming or a second, lighter pass.

Can I toast bagels or buns in it?

Yes, using the high-lift lever to raise smaller pieces. There is no dedicated bagel setting, so use one side of a pair and watch the browning.

What functions does it have?

Defrost, reheat and cancel, plus variable browning on each pair of slots. There is no countdown display or audible done signal.

Pull out the two removable crumb trays under the slots and empty them. Wipe the steel body with a damp cloth; never put the toaster in water.

Is it worth it over a cheaper four-slot toaster?

You are paying mostly for the design and the dual controls. A basic four-slot toaster toasts about as well for far less, so buy this if the look matters to you.