They barely work at all, it's only autocorrection that makes them tolerable. And if there's any moisture on the screen then the input will be erratic and useless.
I've just checked and I can comfortably type on a phone at over 25wpm. That isn't blazing fast, but it's within one standard deviation of the average typist on a full-size qwerty keyboard.
It's not great, but I'd certainly call it good enough. The gap just isn't very big between typing speeds on a touchscreen or a small physical keyboard. I think the market bears that out - physical keyboards have all but disappeared from mobile devices, because they just don't add enough value for most users to justify the added bulk or the reduction in screen size.
Incidentally, wet finger tracking has improved massively over the last couple of years. My current phone works pretty much impeccably even if it's soaking wet.
https://imlocation.wordpress.com/2007/12/05/how-fast-do-peop...
Typing on a phone feels like having both thumbs tied together behind my back, with one finger broken. One reason why I'm so excited by the Gemini PDA is that it might not feel that way.
This happens several times for every sentence that isn't pure English literature and includes some kind of custom caps, word, abbreviation, number, code, contraction, name, or whatever.
https://www.indiegogo.com/projects/keyboard-mod-a-physical-k...
When the Series 5 was launched, there weren't a lot of good options for text input on mobile devices. The keyboard made a huge difference, because your alternatives were a full-size laptop, Graffiti on a Palm device or the awful resistive touchscreen on a WinCE device. The Psion 5 was the most useful productivity device that could fit in a coat pocket.
Today, touchscreen keyboards work well enough that a Psion 5-sized keyboard isn't a vast improvement. For less than $30, you can buy a folding Bluetooth keyboard that is barely bigger than a phone when folded, but gives an almost full-sized keyboard when unfolded. The Gemini's fixed keyboard makes it impractical to use as a phone, but isn't as good as a folding bluetooth keyboard. Loath as I am to admit it, I think it's simply an obsolete form factor.
If the keyboard snapped on magnetically, I might have given it serious consideration. As it is, I just don't see where such a device would fit into my workflow.
https://www.amazon.com/iClever-Portable-Keyboard-Bluetooth-W...