I tried the Winged Slime for Wings in a the Mount Slot instead of an Accessory Slot and it made The Twins go from worst of the Mechanical Bosses to literally flying circles around them and beating them first try on Master Mode. The vertical speed is insane! It also made The Destroyer fun by letting me use The Destroyer as my arena for fighting The Destroyer. (Also, with all Warding Accessories and a Heart Reach Potion, you can stay still and fire the Daedalus Stormbow with an Endless Quiver and win.) It's doesn't have infinite flight, but that's not much of a problem with its falling speed and bouncing on enemies can occasionally save you from hits from below. I honestly don't think I'll ever use wings after the Queen Slime again and it makes infinite flight mounts feel slow enough that I might only use them for building. Depends on how good the Cute Fishron is in an arena of Bubble Blocks and Honey is if I get around to testing it.
The biggest flaw is it can let Plantera pin you to the ceiling if you're not careful, but you can dismount and remount when you've fallen far enough away from her. That sucks, but getting hit two or three times on the way down beats getting hit until you die.