If you're looking for a polished mobile SSH client without a subscription model, you might be interested in Blink[1]. It's worth mentioning that in addition to SSH, it also supports Mosh[2] (it's the official iOS client!), a remote access protocol tailored to handle spotty mobile connections. It's also open source[3] and gives you access to several Unix commands offline.

[1] https://www.blink.sh/

[2] https://mosh.org

[3] https://github.com/blinksh/blink