It's myPhone Pocket, Android 6, 512MB ram, 4GB flash. I found it now cheapest for €42 [1], year ago I found it for €39. The only downside is that default apps cannot be uninstalled, that makes the phone almost unusable. It was never locked to any carrier. It's dual sim but I never had sim in it, I use it only as pocket-wifi-browser (102 grams!) and for app development.
BestBuy has "disposable" androids - probably subsidized by the carrier they're locked to. Just checked - $25 for an ATT phone, used to be $30/$40 with/without sale.
On a high end phone such as yours, it should not be all that surprising that the performance is good!
On my low end Samsung J3, it is rather choppy, but I feel it can be improved, given that this animation is lovely and smooth: http://campoallecomete.it/#!/en
I think people assume rather quickly that animation in a mobile browser will be janky. Truth is, if done well, it really doesn't need to be.
Same goes with me actually. I'm not entirely sure but I think most of it is attributed to the huge amount of optimisations and refinements that have gone into the modern mobile GPU's. While the mobiles don't seem to be quite as diverse in their capability, they excel at what they can do!
Was a present, and is treated as a play thing. General low level use gives about 6 hours, browsing and word etc, but if pushed by a game or couple of vbox nix v-machines (just to see if it could) about that 4 hour mark. As a secondary device it's not been a problem, and it charges pretty quick.
It's a nice thing. Best feature is the flap, imo. all tablet-like devices should have them! I've not got the proper keyboard, but am tempted.