Using DBM double elments

Am I required to use DBM style double elments when they are on the army list? Like the 6Kn in III/64

I understand that the list is designed to make DBA armies compatitable with DBM, but elements like 6Cav or 8Bow have serious disadvantages over the standard 3Cav or 4Bow (like taking up twice as much space on the crowded deployment area or doubling recoil distances)