Custom Harmonicas - Summation
Lastly, everything's just easier to play on a custom harmonica. The big one is that bending is easier (draw, blow and overbend) and the middle bends are less airy in tone. When playing a 3" you'll notice that there's an airy quality to the bend... this is normal for all harmonicas, but is greatly diminished with a custom harmonica.
Okay, let's review...
Balanced
Same breath for each reed, making playing across the range of the harmonica effortless
Dynamic Range
The main reason for playing custom harmonicas is so you can play softly, giving you great dynamic range
Longevity
Since your default volume is lower, your harmonicas will last longer
Savings
Harmonicas can be repaired, not needing to be replaced
Technique
Easier to perform with a well-adjusted harmonica
Those are some pretty good reasons to play a custom harmonica!
Reminder #1 - you don't have to play a custom harmonica, the harmonicas built today (my favorite is the Hohner Marine Band Crossover) are fantastic, BUT if this a passionate hobby and you don't mind spending some money for instruments that make your hobby more pleasurable... go for it!
Reminder #2 - To those that are tense-of-mouth and big-of-bellow... custom harmonicas require good technique to operate. If you play with an overly-tense embouchure (mouth, tongue, neck, shoulders, etc.) and play loudly, when playing a custom harmonica it will sound worse than a stock harmonica and you'll destroy it. You can be rehabilitated though! Focus on relaxing your embouchure and letting your tongue do all of the work. Focus on playing softer and letting the amp do the work if you need to play loud.
For those interested in trying a custom harmonica I recommend the Filisko Guild of harmonica customizers here: http://customharmonicas.com