"What's the best tuning temperament for POWERBENDER?"
My favorite altered tuning is Brendan Power's Powerbender tuning.
To me, the most important feature of the diatonic harmonica is the sound of bent notes. Powerbender offers you powerful, juicy draw bends on all ten holes. There are no blow bends, nor are there any overdraws to play.
All of Powerbender's draw bends are dual-reed bends which means both reeds collaborate to make the sound. You get a much stronger and smoother sound than you get from single-reed bends like overblows and overdraws or half-valved bends.
PowerBender holes 1-2-3-4 are the same as Standard Richter. Ten reeds are re-tuned to provide the note layout.
You can order pre-tuned Powerbender harps but sometimes the fastest and most economical way to go is to convert a Standard Richter harmonica. The conversion to Powerbender is a pretty big job. Some notes need to be lowered by three or four semitones.
Here is a visual aid to the modification:
These note changes can have an impact on how well the harp responds but this is nothing that can't be fixed with a little reed adjustment.
But since reed adjustment will impact tuning, where do you start? The best strategy is to make the coarse tuning adjustments before you do reed work.
Here is a sensible method for getting this done with the least amount of wasted time and effort:
1- Swap blow/draw reeds 9 and 10.
2- Correct factory defects.
3- Perform coarse tuning adjustment. Lower pitches using BluTak or Solder. (See semitone offsets in red)
4- Perform other customizing and improvements including reed work.
5- Perform fine tuning. Identify Major Chords for Just or Compromise tuning. (See scale interval to help you achieve harmonic tuning.)
If you tune your instrument for the major chords, Powerbender layout offers you some new intervals (fourths and sixths) to deal with. These intervals are not part of Standard Richter tuning so you may have never had to tune them before. Thirds, Fifths and Sixths can make the harp sound very powerful when tuned in harmony.
But those notes can sound out of place as melody notes if you have sensitive ears and play in many different positions.
Should you even worry about temperament? Should you just tune everything to ET? It depends on your needs and preferences.
If you play in First, Second and Third positions almost exclusively you may benefit from tuning these intervals in harmony. If the melody notes of most off-the-shelf harmonica are too far out of tune for your ears, go for ET with Powerbender.
Final note: Brendan Power uses half-valving (or even extra reeds in his X-Reed harmonicas) to achieve chromaticism. I just don't connect with half-valving.
I prefer a strong connection with a responsive harp. I prefer playing the missing notes as overblows (there are no overdraws on Powerbender!).
You can have it any way you like.