We don't make that comparison often because planars are typically used for speakers and headphones but not so much in IEMs.
We often use the words "tight" and "fast" and "well -controlled" when describing the texture of the Bass of planar AND BAs, but they are somewhat different in terms of decay and presentation if you pay close attention to them and listen side by side. However, this is really hard to describe in words as if I were to describe how vegemite tastes like to someone who never had it before. You just got to try it.