I had been using the iQue 3600 for a year, then upgraded to the iQue M5. The M5 is far superior to the 3600 in terms of battery life, reliability, and software stability. I keep the M5 charging in my car adaptor, and the life is at least double the 3600. I haven't run out of juice yet while on a cache hunt. About durability: haven't dropped the M5 to a hard surface yet, but I have dropped it on to soft surfaces without failure. I keep a good grip on it when in the field, and move it to my pocket when climbing over logs or over rivers. For paperless caching, one cannot beat the M5 in my humble opinion. Plus, it is synced to Lotus Notes at work, so I have my entire work schedule, contacts. and geocaches always with me. It works well as a navigation tool in the car, too. Now, if it just had a phone. . .