Are the earnings same as or higher than credit sales?
I've had one subs sale that I know of (it happened last Sunday, a slow day, and on a file that went from 2 to 3 DLs, so it was noticeable that the royalty was very low).
It ended up (2 days later when the sale cleared) being 95 cents for a medium. That's less than many of my recent medium sales, but the actual commission varies depending upon how much the buyer paid for their credits.
IS said in the promo stuff that you'd never make less than 19 cents a credit (as an independent); what they didn't say was that with per image sales you frequently make much more than that, but with subs sales, you'll very often make exactly that. The weekend "lottery" will be the fun part - if and when we get to see that. It could outshine ELs in the extreme cases.