The diatonic scale harmonicas are for us musical dummies. We don't have to know anything. But we do have to own a separate harmonica for each major key in which we plan to play. We could own as many as 12 harmonicas though I think you will find that 5 or 6 cover just about every song you will ever play. You can easily get by with just a C and a G harmonica if you are not going to be playing with a band.
Think of it like this. If you are looking at a piano keyboard there are both white and black keys. If you play a song in the key of C you will only play on the white keys. However if you play in the key of F you will have to play one black key. A diatonic scale harmonica in the key of F will have this black key already programmed in. You will not have to change the tab numbers to play in the key of F if you are using an F diatonic harmonica.
Musicians who play other instruments require many months, often years, of practice to learn how to transpose a song from one key to another. Not so with the diatonic harmonica players. They just need to pull the proper harmonica out of their pocket.
The chromatic scale harmonicas require a little more knowledge about music theory. If you have ever played another music instrument before, you might find that the chromatic scale harmonica is for you. Even though they are more expensive, you will not need a separate harmonica for each key.
There are also many songs that cannot be played on the diatonic scale harmonica, simply because there are missing notes on the diatonic harmonicas. You will be able to play any song on the chromatic scale harmonicas.
Back In The Saddle Again
Ballad Of Davey Crocket