Cons
Requires materials to construct.
Might need to buy soil–gardening in the ground is free.
Roots dry out quicker in a hot climate.
Lack of mineral content in bagged soils.
Use of peat moss in bagged products.
Unable to truly embrace the “no dig” philosophy: despite best efforts to the contrary, it seems the soil needs to be swapped out every few years. It’s container gardening, really.