If price is not an issue, it becomes why not. Get both and sell the one that you don't like (Or keep both, they're fairly different animals) . Fit and price were my deciding factors against the Z1R. Otherwise I probably own one alongside the u12t.
The driver distribution is a bit more nuanced it seems, from
@mvvRAZ review: the Z1R's DD actually performs the lows and mids, while the BA covers the upper midrange and lower treble. The second DD covers the ultra highs
So part of the treble is is done by BA. Still prefer the TIA setup though.