WIY,
The steel bowl that they’re selling for $79.99 is a steel version of the plastic bowl. For challah you need the Steel bowl that mixes from the bottom. The dough hook from the plastic bowl will NOT work on the Challah steel bowl. You would have to buy the bowl with a cover and a dough hook and that one they’re selling for $169.99.
A Bosch complete with BOTH bowls and dough hooks is $450.00 from them & $500.00 where I sell it.