Excellent! For a game that is pretty heavy on keyboard use it seems to make sense especially when crafted items will often need to be transferred immediately to the hotbar, it's just one less step.
if there is an empty space in the hotbar a crafted item will automatically be dropped in the hotbar. in crafting you double click the item you like (+the shape in case of building elements) and then its in your inventory. afaik there is no drag&drop. so even if you can open the inventory while in crafting menu you still can´t place a crafted item where you like and still have to go to the inventory to do that.