As some said, the benefit of the Sparx is consistency and convenience. I used to sharpen FBV on a Blackstone prior to owning a Sparx, and I loved it. Nothing bad to say about it and it definitely produced better/cleaner edges. Blackstone makes a great machine. BUT, you have to know what you're doing, it takes more time, and yet there were occasions where I would still mess up and have to re-do everything. Eventually, loading a skate, hitting a button, and walking away and getting a 9 out of 10 was much more worth it to me than spending more time fidgeting with settings, checking marks, etc for a 10 out of 10 sharpen.
Not surprisingly, pro EQMs use both. Sparx to establish the hollow and then a conventional sharpener to get a final finish.