For the past 2.5 years, I've been a PalmOS software developer for the University of Michigan's Center for Highly Interactive Computing in Education. (Hi-CE) (shameless plug: http://www.handheld.hice-dev.org/) In this time, I've spent a lot of time using various PalmOS handhelds--I'd estimate at least a dozen different models. In my experience, the m100 and m105 are the worst Palms I have ever used. I have to use them occasionally to test software on for compatibility, but it's never a pleasant experience.
The m100/m105 (the 105 is basically the 100 with more memory, but otherwise basically identical) comes with the standard suite of Palm software (Address Book, Date Book, ToDo list, Memo Pad, etc), which is, in and of itself, simple and easy to use. As far as software goes, I would recommend a Palm device over a WinCE/PocketPC device. The Palm apps may look simple and underpowered, but this is their strength. Palm software follows the Unix mantra of "Do one thing and do it well." What Palm wants its software to do, it does. It's all very straightforward and easy to use, and I've seen classrooms of 3rd graders using the Palms like pros after half an hour.
That being said, the m105 is not a device you want to experience the software on. The m105 is a "low-end" PalmOS device, and it undershoots even that mark.
First of all, the screen is smaller and harder to read than on other Palm devices. While it has the same 160x160 resolution as other Palms, the screen dimensions are smaller, making each pixel smaller. Additionally, the screen is noticeably fuzzier and has poorer contrast than other devices. All in all, it doesn't make for pleasant viewing. I've read (short) eBooks on my Palm IIIc; the only person who would be happy about reading anything lengthy on the m105 is your optometrist.
The input function of the screen is met equally poorly. The m105's screen seems to be of softer plastic that the screens of other devices, and this (or some other factor) means that the touch-recognition isn't as good. While it doesn't make a difference when you're just tapping on icons and opening calendar entries, it makes entering information much harder, and even interferes with things like using scrollbars easily.
The rest of the body of the m105 is almost as low-grade: while I've never seen the actual casing broken, the screen covers break at the drop of a hat (let alone the drop of the Palm), and the stylus is horrible. While devices like the IIIc come with a very nice, metal-bodied stylus with a plastic writing tip at one end and a screw-off reset jabber on the other end, the m105's stylus is just a single stick of plastic. It's less pleasant to hold, it flexes when you're writing with it, and, if your Palm needs resetting, you have to hunt for a paperclip rather than just unscrewing the end of your stylus.
The crowning unpleasantness, though, is beaming. The m105 seems to have much lower-quality beaming than either its ancestors or its followers. I think the IR port for the m105 has less power than the ports on other devices, and it is in an inconvenient position on the body of the Palm. Sending an application from one m105 to another involves a tedious process of aligning and realigning the IR ports just so and becoming very familiar with the error message, "Beam interrupted; please ensure that the other Palm is in range and correctly aligned." With other Palms I've used (particularly the III series), pointing the Palm in the general direction of someone using an equally decent Palm is enough for a successful beam.
All in all, I'd suggest that someone looking to purchase a Palm stay away from this particular device. If you're looking for a cheap handheld, try the m125 or, if you can find one, the Palm IIIc (you'll have to get it refurbished; they don't make them anymore). Both are close in price and of much higher all-around quality.
Note that I haven't listed a price; I have never bought a Palm--they're just thrust at me with the order, "here, make sure it works on this"--so I don't know how much we pay for them.
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