Older Birdy had a square taper BB. the Hollowtech of the gen 3 was chosen because it weight less and is more reliable, its a pity to go back to a square taper.

The drawback of the square taper type are well known: its often creaking, there are two different sizes, JIS and ISO that are not really compatible and more over most manufacturers do not accurately follow the specs with as consequence that often cranks and BB of different manufacturers, supposedly of the same type, in practice do not fit well.

Its the reason for the development of the ISIS BB.