Size - The device with cartridge attached is about an inch longer than an iPhone. With the cartridge detached it breaks down into two pieces smaller than a cigarette. It fits comfortably in a pants pocket. Durable ? The OPen is made from metal. The cartridges have plastic but they are disposable so it?s expected. The cartridge and device have a threaded metal connection. Stylish and Sleek ? It looks cool and has a small profile. When taken out in public people either don?t notice it, or find it intriguing and mysterious. Battery Life - Even with daily use, users can go 3 to 4 weeks without having to recharge the pen. This is one of the most impressive parts of the pen. Cartridges - Cartridges are easy to change, strain specific, and come in Sativa, Indica or Hybrid.