Does anyone grow?
Tropaeolum tuberosum very pretty flowers edible root.
Jayb is the one to ask. I grew it one year but only got two small tubers for all my efforts. Didn't eat them as I wanted to use for seed but they shrivelled up into nothing.
Easier to say the common name; Mashua! Yes, I've grown it for a few years. Some people find the taste disgusting, others like it. Pilifera is probably the best variety for eating tastewise (possibly a subspecies I think). I've posted about mashua in detail here:
http://oca-testbed.blogspot.co.uk/2012/12/more-mashua.html (http://oca-testbed.blogspot.co.uk/2012/12/more-mashua.html)
There are more productive crops to be grown, so only worth considering if you have space to spare, but it's pretty maintenance free, resistant to bad weather, and can be grown amongst other taller crops. The flowers only come very late in the year, and may not beat the frost.