Short summary: I love the watch, but hate the heart rate strap.
Longer list of positives and negatives...
- Long battery life (approximately 20 hours). This is important for longer ultramarathons (anything around 50 miles or more) and extremely long training runs. The old watch would barely made it 8 hours. Now I have a great cushion of 20 hours--should be good enough for every race except 100 milers...unless I run my next 100 in under 20 hours!
- Waterproof to 50 meters. Not a big deal for me since I'm not a swimmer or triathlete. It does give me greater confidence when running in the rain or crossing deep creeks where my hands are under water. Yes, I've had river crossings were the water was well above my waist!
- Slightly smaller size than 305 (but still rather large). Not a big deal since this isn't meant as an everyday general watch. Still, it's nice to have a slightly smaller watch for running. I do like the large face for seeing all the data during and after runs.
- Wireless ANT+ data downloads (thanks to that little USB stick in the above picture). This is a great feature! Love that it automatically downloads when close to the computer (and automatically uploads to Garmin Connect). Yes, I am lazy.
- Auto upload to Garmin Connect. Related to the ANT+ downloads. Pretty cool that it then uploads to my Gamin Connect account. I'm going to be getting really lazy soon.
- Both vibration and tone alerts (HR, pace, distance, etc). You can pick alerts for pace, heart rate or distance and have audible alert (tone), vibration alert (watch shakes), or both. I use the vibration alert--it works great and I don't bother my running companions with the "excessive HR" beeping.
- Auto pause feature (pauses timer when you stop, auto start again). If I stop to tie my shoes or get some water or talk to a friend on the trail, it pauses automatically. And starts again when I begin moving. I am definitely getting lazy!
- Quick lock onto satellites. Faster than the 305. Never was a big issue, but it's nice that it works a little quicker.
- More data screens on watch (4 screens, 4 pieces of data each). 16 pieces of data at my finger tips--and there's an option to automatically scroll through all screens as you run. Nice.
- More data choices to display (love the current and average % heart rate reserve). I use the current heart rate, average HR, current heart rate reserve, and average HRR as my main screen.
- Premium "soft" heart rate strap that digs into my chest on every run, with serious chafing, often drawing blood! The older plastic strap was not the most comfortable, but it never really chafed. This new one is ridiculous. Searching the web, I found this to be a common complaint...with a fix. (Full description of problem and solution can be found on DC Rainmakers' blog post.) Basically, you tape the plastic transmitter and lower section of the soft strap so it can't dig into your chest. I've now used the tape fix on several runs with success. Why should I have to "fix" a brand new premium soft strap? What's wrong with Garmin?