Word Flow is a “swiping” keyboard, where you don’t pick up your finger between letters, and it has an “arc mode” that curves the keyboard for easy typing on one corner of the screen. Nifty!
I haven’t had much luck with third-party keyboards on iOS. Apple wants you to use them for occasional, added capabilities. It doesn’t want you to set a third-party keyboard as your default. This is one area where Android beats Apple.