Grid will place your objects next to each other, so you don't have to set an exact position.
With the addToRow function you add the object to the right of the previous object and you can use addRow to go to the next row. The addToRow function also optionally takes borders as parameter to put some space between objects. So Grid can be used to make a menu screen by placing buttons beneath each other, without you having to worry about the exact position of the buttons. But Grid doesn't change the size of the objects, you have to set the size yourself.
Although Grid can be compared with the layouts from qt, it still has a lot of limitations.
Support for real layouts is pretty hard. I mostly have to consider how it will be designed, which functions it will have, ...
So this can't be expected before v0.7.
The stretched text is indeed problematic. Depending on where the text is you could draw it with sfml directly with a different view than the gui, but that isn't a great solution either.