I have Filterstorm Neue on my iPad -- redownloaded it several months ago. It still works now, but it doesn't show in my llist of purchased apps anymore, so if I delete it, I assume I won't be able to download it again. (Don't know if it'd be recoverable from an iPad backup or not.)
There were three apps: first Filterstorm, then Filterstorm Neue, and finally Filterstorm something-or-other, Neo maybe, which I seem to remember was subscription. None of them show in the App Store now. I don't use it at all now and don't remember why I downloaded it again. Maybe for its ability to resize each dimension independently, regardless of aspect ratio?