What's the maximum span for a regular kitchen worktop?
On the plus side you have linked a solid timber top, and those are stiffer than most composite types. On the minus side, 3m is quite a long span for a 28mm thick slab of wood. Some sort of support in the middle would probably be advisable - a leg would work, you could also run some sort of beam under the top, or use large brackets to the wall (if you'd prefer to keep the floor under it clear.)