I've not tried the bags but I had to potato plants that you could just slide a panel up to get at the potatoes without having to dig up the whole plant. I didn't find them very successful although what we did harvest were very nice. It was the quantity of compost I had to buy to keep earthing them up that got me as well. I then tried using old food sacks with holes in the sides to let water out and they were no better for the same reason. If you can fill them with soil rather than buying compost, it would be more worth while. I just couldn't justify £10 worth of compost for a kilo of spuds. They weren't that nice. I did better with the ones that grew from peelings in the manure heap.