Its a great device to experience the foundations of handheld computing. You'll get to see firsthand where some of the ideas that still exist in today's modern mobile phones came from. Its a piece of technological history.
Apart from that, be prepared to be disappointed with using it as a productivity tool. I got one secondhand in the late 1990s, and even then it was worthless as a productivity tool. The original model was significantly worse than the later ones.
The handwriting recognition was particularly horrible. This is one thing that got better in later Newtons. The battery life was also horrible. Even with the monochrome supertwist screen it just didn't allow for any long run time of use, and that was on functioning batteries from the day. I don't know if there are any modern replacement batteries using today's technologies.
Data transfer to and from the device was REALLY SLOW. If memory serves it was an RS-232 serial connection that topped out theoretically at 112kps, but was unreliably at that top speed requiring force drop in speed to 57.6kps or 38.4kps.
Don't forget, its large and heavy by today's mobile computing standards.
There's a reason that Palm PDAs and PalmOS ruled the 1990s and Newton didn't. You're about to get a front row seat to that experience.