Esker
Hero
As far as the balance goes, you are gaining two traditional levels for two traditional levels.
How so? Say I'm a rogue and I'm deciding between taking the swashbuckler subclass and multiclassing into fighter. If I take swashbuckler, then I get the subclass features attached to the traditional level 3. If I multiclass, I get the benefits of the L10 1st level of fighter, which is more or less worth two traditional levels. Right? Or am I misunderstanding?