Planet Computers' Gemini PDA has been my sole phone, communications and portable computing solution for a whole year. In that time, it has met my expectations and more - I am well pleased with my purchase. But there are some qualifications, largely in software, support and Linux. But first, the hardware:
There is one overriding reason to buy the Gemini - the clamshell design with a 'proper' mechanical keyboard. I am writing this review on the Gemini. The keyboard is a solid performer, if rather too small for ten-finger touch typing. I have found that the best and fastest input is from the use of only three or four fingers and thumbs. It's not touch typing but it achieves the best balance between speed and accuracy and makes the Gemini keyboard a joy to use.
The clamshell design has stood up well to many openings and closings every day and seems to perform just as well as when it came out of the box. My only criticism being the sharpness of the metal edges around the closure points (once bitten, twice shy). The case has worn well and, although it is obviously not new, it is free from any major scratches and blemishes, despite sharing my pocket daily with sundry other metal objects.
Other users, however, have reported issues with cracked hinges and less than optimal keyboards. It is hard to pin down the reasons for this - perhaps there is manufacturing variability and perhaps differences in how the device is handled. I can only report on my own experience, which is very good.
Planet Computers software is another matter. Notes, Data, Agenda, Airmail as well as a number of utilities come with the Gemini. Personally, I don't think that Planet Computers have the resources necessary to develop good software. The applications tend to be clunky clones of old Psion software and in my view are, quite frankly, best avoided. Fortunately, there are many Android apps to choose from which perform very well on the Gemini, and much better than the Planet versions.
Many people bought into the Gemini on the promise of Linux compatibility. They have been mostly disappointed. Linux is available on the Gemini, but it is reported as awkward and incomplete (I don't use it myself). Having previously spent a lot of time with Linux, my feeling was, and still is, that Linux is largely for hobbyists, hackers, servers and black-box systems. If companies like Canonical struggle to produce an open-ended, consumer-grade Linux OS, then there is no hope for a little company like Planet Computers. Try Linux if you like tinkering, otherwise just stick with Android.
Mostly, Android runs well on the Gemini. But Planet seems to contract out their Android integration to a less than wonderful company. Android updates are best avoided on first release. Expect to wait a couple of weeks after release, until other (braver) users are reporting that it updates and runs ok. While my Gemini runs well on Android, in the last year I have also experienced loss of functionality on the silver button for several weeks and Google Maps ceasing to operate for a while. These were addressed eventually, but I won't be rushing to update to Android Oreo until I hear that the road is clear.
Planet Computers suffer from poor communications and patchy support. They let issues fester before making any public statements about them (Apple do this too). They over promise on dates and regularly under deliver. Support seems spotty; some users report being very happy, while others can't get any response at all from suppport. All this could be put down to Planet Computers being a startup. But, two years down the track, things should be getting better and there is no evidence that it is.
If you are likely to need hand-holding or have high expectations of any company you do business with then you may want to avoid Planet Computers - at least based on current evidence.
I like my Gemini. It fits my style of working perfectly and is the natural successor to the Psion PDAs and Nokia Communicators of the early 2000s. I have the next version (the Cosmo Communicator) on order so that should tell you how pleased I have been with the hardware. Would I suggest it for my non-technical family members? Probably not; it does occasionally require some basic troubleshooting to deal with, or work around, a software issue. If you aren't comfortable with that then the Gemini might be best avoided.
To keep things in context; there are some downsides (mainly software reliability) but for me, they are outweighed by the considerable upsides - it fits my lifestyle and, quite frankly, there is nothing else available that can come close to replacing it. I hope that the Cosmo Communicator is at least as good as my Gemini.