I have used the Mini-pac in the past and they are great.
If this is your first one, or you don't like to hack cables, buy the harness, but be sure to get the one that allows for the kind of trackball you plan to use. The harness is kinda expensive, but well worth it to save time and trouble. The software is pretty easy to use, but you don't even need it unless you plan to re-map buttons.
I have not used the other encoder, and it is probably a good product too, but I had the same CP setup, 2-layer, buttons, trackball, and spinner, and the mini-paq worked flawlessly.
Good Luck!