If feeding jus pig nuts it isn't really economically viable, but still worth it.
I keep 3 at a time and butcher them every 6 to 8 months, I live next to a big fruit farm though, and have them registered on both sites, and rotate them on both sites, so I can feed them the farms by products, making it a lot more viable.
One thing i will def say for them, they are far easier to keep than I was imagining. Once you invest in the right electric fencing ect, the costs are minimal.