Been using this for years, haven't found a better program if you wish to view manga vertically, just scrolling down, only found 3 flaws.
1º Fails to open some zip and rar's, when inside them is a folder, instead of just all the images.
2ª Crashes on big folders, unreliable on folders above 200mb.
3º If you have in one folder, subfolders as well as images, it's impossible to browse just those images, the software only shows you the folder inside.Ohh yeah, it also plays gifs! (no WEBM though).