A friend of mine is doing this, now in her 2nd year. She has physical disabilities, has plenty of room, access to cheap hay (she's experimented and decided hay is better than straw) and friends to help her set the bales in place. For her, I guess it makes sense. To me, it seems like a lot of work and expense for a relatively low yielding garden and I wouldn't be interested in doing it.
Yeah it is a lot of work for low yield, but my property is on a steep hillside with few decent garden spots. The best flat, good sun area happens to be where the builder placed the septic and drain field, so growing above that, in bales, makes sense, since the soil is a no-no. Any safe method of utilizing that patch of land gets my attention.
I contacted the company and asked if hay would work, instead of straw. I wanted some clarification, since their web page seemed to emphasize straw. They said it really makes no difference, so long as you followed the preparation stage of nitrogenating the bales of whatever was at hand. I am also thinking that alfalfa bales might be a great medium, since it is such mineral rich plant.
Its a little late for this project this season, but I may try a bale garden tobacco experiment next year, over the septic field, with some plastic sheeting between the bales and the ground. I can probably get 50- 60 plants in the area that is currently unused.