The Ttsx and TSX bullets are different beasts to the old X bullets. I have found the TSX group as well as ANY other bullet I have tried and better than most. The X bullets of the past could be a bit fickle though. I believe that this is due to the pressure relieving effect of the bands on the shank of the bullet. I think it is also important to recognise the differing expansion properties of the copper bullets. In general each bullet will behave like a heavier lead core bullet would do. Consequently to match performance of a 150g 308 lead core bullet, a 130 grain TSX would be appropriate.
To be honest most people who post about them seem to be converts to the concept and the sceptics appear not to have use the bullet in anger but merely don't like the concept. Cost could be an issue as well but the cost pales into insignificance compared to the other stalking gear and is mitigated by the reduced meat loss