tensiles, to my knowledge, have been out 2 years. It was their first design, and for a first design it was bloody good.
middleburn have been making cranks for 15 years, the RS7's have been around for about 5. Theyve had time to get the design right, and particularly in the earlier days far fewer people jumped and shouted about them breaking.
my burns are 2 years old, they still look fine, the tensiles in that pic have been abused in a fashion that would have killed a set of middleburns too.
tensiles are cheaper and more versatile than burns, backed up just as well, and will withstand rough treatment far better.