There are 2 sides to this one.
I found that in my fairly heavy soil, they struggled. You need the top growth to go mad and flop over with the weight of all the leaves to get big tubers. Mine grew, but were no-where near that vigorous.
Slugs are an issue as well. You have to let the tops die right down and then leave it another few weeks, for the tubers to really swell up. That meant harvesting pretty late in the year and slugs had been having a go. I know Sunshineband tried them and got better results in her soil to me, but mice and rats are a problem on her site and they also found oca pretty attractive.
Now the good news bit
One of my plot neighbours cadged a few tubers from me and tried them in big pots at home. He reported great results. He used a John Innes/multi-purpose mix of around 50/50 each and kept them well fed and watered. He got lots of foliage and flowers and then stood the pots in his greenhouse to finish growing once the leaves had died down. He had a decent crop of large tubers when he knocked the pots out. It seems a better way to grow them, but I decided I didn't have room for pots of them at home.