As farmers markets go this one is fine, although the range of stalls can tend to be quite limited. In fact on the occasions I've glided over to this part of my hometown, and thinking specifically about fresh produce, I've only ever returned with memories of one single - though reasonably extensive - fruit (possibly vegetable) seller.
There are other traders on the pedestrianzed concourse between the theatre, sushi restaurant, and Jubilee line tube entrance/exit. They do cater to flesh eaters, but they usually serve up other products more appropriate for vegetarians at least. I particularly like the cooked food sections, especially those whizzing up on the spot Thai and Indian meals. I especially like the vegetable fried rice prepared by a group of female and male Thai cooks, which at just over £4.00 for a medium-large box is pretty generous, not to mention very scrummy. I've found the Indian traders' deals comparatively less rewarding - both in price, and only a little less so in taste.
Cons: possibly away from the centre of town., on occasions slightly windswept location, limited stalls.