I love the Stylus, esp. for work on plastic, but I could not do heavy-duty work without my Dremel 398 Pro, which is an AC-powered digital/electronically-controlled model. If I were buying an AC-powered rotary tool now, I'd look very seriously at the models from other makers that have electronic control over the motor speed under load, such as the Proxxon. It makes all the difference when cutting hard materials.
The Stylus is an excellent design, and the pistol grip is great. But it lacks the torque and speed control that the AC units have. On the other hand, the AC powered units are not as easy to point and use as is the Stylus, unless you get the separate handpiece attachment.
All the rechargeable units will have a limited lifespan, but I've had mine for two years and not seen any deterioration in the battery life or performance.