Two crossbows to avoid ammo switching

I'm trying out going with crossbows as both my primary and secondary weapons for my Mercenary. I have Permafrost Bolts loaded and fired by my first crossbow to freeze enemies, and Fragmentation Rounds from my second one to explode frozen enemies. This saves me the time of having to manually switch between the two types of rounds, and switching weapons is instantaneous and switching ammo types are not.

Is this a common strategy for crossbows and/or bows to avoid having to constantly change ammo types?