I have contacted HR and they said:
"Once you apply, you will receive an online blended assessment, comprised of short cognitive ability tests (numerical, verbal and logical), and questions around personality and motivation."
They did not, however, say whether it was CEB SHL or Cubiks or something else entirely.
Two further questions:
1) Is the test as equally difficult than PST/BCG test, or is it slightly easier (calculator allowed etc)?
2) Does Bain then give an on-paper maths test at their office like McK & BCG?