I used a KaiOS device for about 6 months. My expectations weren’t high, but texting and T9 input were a mess:

A) I had to manually enter captital I, apostrophe, and ‘m’ every time I wanted to write “I’m”.

B) New words (like brand and place names) displace common words in the built-in wordlist - that is, T9 gets worse the more you use it.

It was still an OK digital minimalist/detox device - the GMaps web app with voice search was good enough.

The Android Go devices you mentioned sound far better – I’m never touching KaiOS again.