Would you say it was worth the coin?
I'm on the fence on this
I'd say it depends. If you are processing large volumes of brass for sale or use, I think it is worth it. Decapping first will ensure you have smooth reloading on your progressive. It should minimize ringers and other stoppages during loading. If you are just a casual shooter with lower volumes, then I'd stick with decapping on the press or whatever process you are using.
Pro's:
You can decap before you tumble your brass. This minimizes any ringers from the brass not fully drying out and the primer corroding in place. It also speeds up the drying process.
If you use stainless media, the pockets will get cleaned if you decap before tumbling. If no stainless media, the pockets will get cleaner but not spotless.
If you are rollsizing, it minimizes the brass dust from the primers that protrude and scrap along the base of the rollsizer. This also gives more uniform rollsizing as all the brass sits on it's head vs some that ride on the protruding primer.
Decapping before loading does reduce OAL variability on a progressive due to some stubborn/crimped primers not wanting to decap (changes the shell plate load distribution).
Con's:
It's an extra step in the process, that you can't really walk away from while it is running.
The decapping pins on the FW/Dillon decappers are not cheap and are a consumable (turduken cases, beridian primed cases, rocks, tiny flash holes, etc will cause stoppages).
If you want to keep your primary loader case feeder clean, you have to either have a dedicated decapper case feeder or tumble the brass before decapping (kind of defeats the purpose of the machine).
Cheers,
Toby