Top 250 Contributor
The pro version allows you to independantly adjust and set up the front mech. Once you are happy with the shifting performance you can then fit the chain catcher and set its position with its own lock screw.
With the standard version, your one front mech bolt holds both the mech and the chain catcher, so you need to get two rather different things aligned and set up. Its a bit of a faff doing it this way, so the pro is much easier and gives better perfomance as each part is set up independantly !