I have used Safari Cookies for years and when it was not getting updated past 2.0 and wouldn't work on my system anymore, I decided to support the developer and purchase Cookie. (Albeit the MAS version, where I realize Apple takes a cut) And I've never regretted that purchase, until now.
Now, while Cookie still functions, it appears to either be at or approaching EOL only a couple months after I purchased it. The main reason I bought it was because I assumed there would be continued updates for a long time to come.
I find this slightly unethical to make users re-purchase the product just because of the relatively small portion of people that are unable to update to El Capitan.
I realize $15 isn't a lot of money for some people, but to others, it's a significant chunk. Especially when you have to spend it again for the same product, when paid-updates weren't even in the scope during the original decision to purchase the software.
There are a couple of better ways the v5 rollout could've been handled. But in light of where we're already at, I'd recommend putting some of those promo codes to use.