These aren't subscriptions, but they are a bit different from SS or other site's image packs - they expire in a week (originally it was 30 days I think, but the site currently says 1 week). So this can't really be used as a credit substitute as easily.
However, I think the appeal for the buyer would be that you get 5 or 10 images, regardless of level, at a fixed price. If you buy with credits you pay more for a level 5 than for a level 0 or 1.
As a contributor, we receive a flat rate, which is quite a bit less for a level 5 image than the rate we would receive on a credit sale (45% for a level 5 image which would be $3.10 royalty on one of the 10 pack images the buyer pays $6.90 for). If the buyer paid with credits, a maximum size level 5 images is 19 credits - about 3 times the price of the subscription pack.
When we get $2 for a $6.90 sale, that's 28.9%, not 45% as a level 5 image would/should get. So it seems to me these image pack purchases are a way of undoing the problems the image levels have created for buyers while also cutting the royalty rate for contributors some more.
It's the death of a thousand cuts - starting at a 50% royalty and simple pricing, then making a complex mess of multi-tiered pricing with most of the promises made to sell us on the changes broken - double subs royalty on top level images, non-subs sales making higher royalty levels as well as higher prices. Finally moving towards undoing the complexity of level pricing without restoring the royalty level back to 50%.
The forum threads were trying to say that the $2 sub is so much better than 35 cents (or 42 for an exclusive) which might sound persuasive, but it's much less so if you look at these "subs" as credit packs where you don't make the stated royalty percentage for the image's level.