Even those are not "true-temperament" instruments like a piano, they adapt a "well-temperament" tuning system like Bach's keyboard tuning [0]. The end result is closer to true-temperament in some keys, and farther in others.
Oh, and that applies to standard tuning only. YMMV with alternative tunings, especially the open tunings.
Oh, and that applies to standard tuning only. YMMV with alternative tunings, especially the open tunings.
0: https://www.guyguitars.com/truetemperament/eng/tt_techdetail...