The Handspring Visor only recently made its debut in the PDA arena, yet it's already crowding Palm's market share.

So what's the secret behind the craze?

Buyers are loving the Handspring's Springboard, an expansion slot that allows easy snap-in installation of hardware and software modules. From modems to memory to backup modules, the Visor can accommodate almost everything you need to keep your PDA truly multitasking.

The springboard looks like a typical PC card slot you've seen in notebooks. Extra hardware and software modules can snap into the PDA and run as if they were integrated parts of the device.

And it's simple. Anyone that can run the tiny electronic organizer will be able to use the springboard feature without worrying about installation and configuration processes.

Just slide your module into the slot , and it's ready to run. The software needed is already in the module and installs automatically (and is instantly gone when you remove the module).

The Visor has been rumored to crash a little more often than Palm models, and we've heard reports about customer service - including simply getting the model to you -- that are lukewarm at best and horrific at worst.

But even those users that long for better customer service still can't find much to complain about with the Visor itself. The device is actually very similar to the Palm, running the same Palm OS, coming with the same applications, and having pretty much the same weight, size and look.

There are a number of hardware and software modules already available to use with the Visor, and you can be sure to see more since Handspring has made the bold move of posting the springboard's specs right up on the site for developers to use free of charge.