Personally, I think it would be great if the only difference between just say, the sx900 and sx700 was the harmoniser. Would probably save a few dollars.
I’m pretty sure a lot of people never use it, either because they don’t sing, or because they may prefer a different type.

Only reason I went for the SX900, didn’t want to miss out on the chord looper, extra styles, sounds, better speakers etc .
I sometimes use my monitor speakers, my headphones ( when I have to), most of the time I just use the onboard ones, they sound good, switch on, ready to go.