Many of my locos have sound decoders. They can have hundreds of CVs.
With DecoderPro you enter the values into the appropriate boxes and click one of the "write" buttons.
Doing the same with a throttle or the MRC device means entering CV mode, entering the CV number, entering the CV value and pressing the "save" key. That is going to be extremely tedious if you have to do many CVs.
For all of my locos I set a speed table - right there it is 28+ values. Even that is going to be tedious doing it one CV at a time.
I also am using the speed table to set the bottom and top speed of the loco and this involves some trial and error. With DecoderPro it is fairly painless.
The MRC device is about $75. You can get a new, entry level laptop for $125-$150. The interface device depends on your DCC system but it's going to be $25-$60.
Unless you really enjoy doing tedious things you will find DecoderPro a much more pleasant experience.
My two cents.