About the only feature I'm missing in Prompt is the ability to sync connections (and thus passwords and keys) between my iPhone and iPad. Some of this is alleviated if you can take the time to set up Agent Forwarding, which Prompt supports, though that's a pretty technical endeavor that most people won't bother with.
At $8, Prompt is probably one of the more expensive SSH clients you can find on the App Store. But that extra cash buys you something: solid engineering; a simple, attractive interface; and great usability. In all the years I've used it, I've never had need to regret my purchase, and if you use SSH with any regularity, you won't either.
Sign up for CIO Asia eNewsletters.