Many people will vote for Komorowski not because they think he is good but to curb Kaczynski chance to become president.
Certainly, most/all SLD voters will do such a thing. Likewise, you might see PSL voters voting for Komorowski simply because he's their best chance of getting PSL-sponsored legislation through.
And even the masses of undecided people will vote Komorowski just to keep Kaczynski out, as you say.