So I have had my Garmin Forerunner 310 for a few weeks and I have to say it is working great. I have ran with it several times, biked with it several times and tonight I did my first brick with it.
The watch is less bulky then the 305, but the display is slightly wider. It fits fairly comfortably on my wrist and has a fairly secure latching setup. The start and lap buttons are slightly harder to press, but that is mainly because they are recessed as part of the waterproofing.
The user interface is slightly improved from the 305, but it pretty much resembles the same interface and has the same button sequences to control it. The 305 allowed many of your training settings such as auto pause, auto lap, and alerts to be set separately from run and bike. Basically if you were in run you were setting run settings and if you were in bike you were setting bike settings. With the updated interface, it is much clearer which sport you were setting. I also felt like there were less menus to drill down through to get to the settings. If you have the 305, then moving to the 310 should be fairly easy, unlike the 405, which Cathy has and I thought was a little harder to change settings.
So how does it work? Very good.
I havent used it on the swim yet. The GPS is not accurate on the swim, but if you are doing laps you can lap it and then fill in the distances manually in sport tracks. The one feature I think I will likely use on my iron swim is the alert. Becuase the 310 also has vibration beside the sound, I can set an alert to go off every so man minutes so I can pace myself accordingly.
On the bike and run, there arent any big changes. The GPS seems to pick up the satellites much faster then the 305 did. There are now 4 configurable screens for each sport. There is a HR Zone graph you can use on one of the screens. I only used the training partner once or twice on the 305. I found the 310's training partner to be something I might actually use. On one screen, you get the icons as well as two fields: miles ahead/behind and time ahead/behind. Other then that, I dont think there were any big changes.
When I did my brick tonight, I was super happy with how the 310 performed. The 305 worked fine for a totally outside brick/ However if I rode inside on the trainer and then ran outside. I would literally have to stop and reset the bike and switch to the run. Otherwise, it would show my speed as something insane in the 100s of mph. The 310 worked almost flawlessly. I set up the multisport just like in the 305. I turned off GPS to save battery. I probably didnt absolutely have to since it should revert to the sensor, but didnt want to mess with that. When I finished my bike, I hit the lap button to switch to transition. Got my shoes on and went outside. Before I hit the lap again to go to run, I had to turn the GPS back on. OT picked up signal in less then 30 seconds an I was off.
Downloading the data is fairly painless. I use Sport Tracks to track my data. It did take a little figuring out how it would work. Basically, when you plug your ANT receiver in and turn the garmin on, it downloads the data and then you open up Training Center or Sport Tracks and you then have to chose to D/L from the ant agent. The most important thing I can recommend is to go to the website in the quick install instructions and download and install all updates before using it. When you update the S/W on the forerunner, it deletes all the data. The only other thing I've noticed is that it downloads much much slower then the 305 did. Not a big deal, just a little bit of a nuisance.
I have not seen a quick release kit for the 310, but I may not even want it. I will need to see how secure it is because I dont want to risk losing it on the swim. Because the HR and Speed sensors only communicate one way (they send out data but dont receive any communication from the forerunner) I am able to use my 305 on the bike as a dedicated bike computer at the same time my 310 is on my wrist.
The calorie calculation function is supposed to be much improved. It definitely looks closer to reality. I havent looked at it any further yet to see how accurate it actually is.