Hidden shelf supports - how strong?

[d000hg]

I've an off-cut from a solid oak table-top I'd quite like to use as a shelf; it's 1m long, about 20cm deep, and the wood is about 4cm thick, so it's quite a hefty bit of wood.

I'd like it to be quite slick and was wondering about using some sort of hidden/invisible bracket rather than normal under-shelf brackets. A google search shows things like this exist:

But I'm a bit worried this would increase the torque applied to the wall, which is a modern internal wall (thick plasterboard on a 'wire' frame) so no bricks or wooden beams. With the shelf being heavy to begin with, is this a bad idea?

 

[d000hg]

The other disadvantage is it means doing more damage to the wood of course...

 

[Burnerman]

Those blind floating shelves are generally pretty lightweight, and its essential that the bracket poles are at 90 degrees......for a chunky shelf, it would be side supports for me.
John

 

[foxhole]

Where is it to be fixed, alcove? just one wall face?

 

[d000hg]

It might end up in a corner but I wasn't explicitly planning it that way; potentially it could be arranged so the length and one end are up against a wall but not both ends.

 

[foxhole]

Unsuitable for plasterboard walls unless there is next to no weight on it.