1/2" and 9/16" are the THREAD SIZES... not the flat sizes.

Typically 1/2" threaded pedals are used on kid's bikes and one-piece Ashtabula cranks.

9/16" is used on almost everything else except vintage French pedals.

Essentially all modern 9/16" pedals use a 15mm wrench (or an Allen Wrench)... Love the mixed units.

Personally I don't use "pedal wrenches". I just use a relatively narrow 15mm wrench.

Keep in mind, if you get one of the super long wrenches, you'll be more likely to tear something up.