I'm currently using it on my RF build. A 6L carcass Jack goes for about 30 Ex, give or take a bit. The only B B B B B R on poe.xyz is over 40 right now because those colors are hard to get if a person needed that combo.
30 EX / 50 fusings per EX = 1500 fusings
From what I've heard, on average it takes about 1000 to 6L an armor, with an obviously massive variance around the mean.
Rule 8: If you don't intend to sell an item. Never craft it.
Rule 9: Equip only items you have found or bought.
Good vaal orbs : http://www.pathofexile.com/forum/view-thread/840813
Bad ones : http://www.pathofexile.com/forum/view-thread/812199
Why? http://www.pathofexile.com/forum/view-thread/854397(I got an answer)
Risk vs reward. You could end up getting the 6 link on the first fusing or it could take 3000. I guess it depends how much currency you have saved up. If you are rich I would totally go for it. If you only have the wealth to 6 link it I would buy one.