Just remembered that the special whip feat IS a multiclass feat, so you can't multiclass into a martial class to qualify for it, and then take it. Nevertheless, its worth using a whip if you feel that going from d8 to d4 damage and gaining reach is worth a feat, or if you feel that spending a feat to lose your heavy shield and gain a reach attack is worthwhile. If you do that, you can at least access two weapon fighting to gain some of your defense back.