It's possible that all the features I use in e1547 are directly available in e621, but I'm too lazy to look into it, that said, I love the 'Subscriptions' feature because I have a Mastodon-style feed with a constant stream of new drawings from my favorite artists (of whom there are probably hundreds). Also, I really like that because if I find an artist I like on e621 I can 'follow' them, whereas on e621 (which as far as I know, this feature doesn't exist) I can just favorite them and if I want to look for them again I need to go through my favorites.

Another thing I like about e1547 is that I have 3 tabs, a "Home" tab where my default filters are applied, for example, at this moment my filters are ~digimon_(species), ~pokemon_(species), every time I open the app I will see the equivalent images that would appear if I search that manually, it's not a big deal but it's more comfortable. Then there is the "Hot" tab that uses the order:rank filter, great for finding new artists in my opinion, and finally there is the "Search" tab, where I can search for tags and they are not applied permanently unlike the "Home" tab.