I've owned a couple of Polar HRMs over time and I like this one the best. The watch itself is very nice. I have small wrists and this one fits my wrist nicely and the strap length is better than in the past. The band to hold the excess strap has a bump in it to keep it on the tail end of the strap. It comes with an extension strap for giant arms or over a coat. The buttons and thier function are pretty much the same as my previous Polar instruments. The display has changed although navigating the menus is in the same style. The top of the display is a matrix of dots so images and text can be displayed. This makes the menus easier to get through for me. When in monitor mode there are configurable screens that can be set up with the software the way you like. The functionality/options are pretty much the same as my prior watch s625x. The battery on this watch is easily changeable. Prior versions required skill and patience to change the battery as the entire guts of the watch had to be dissassembled - this new approach is a welcome change.
The stride sensor: the things I was interested in are: cadence (steps per minute for one foot), speed, distance. One has to calibrate the sensor. The watch allows for three calibrations for three pairs of shoes. As with any sensor like this the calibration needs to be done at the speed you use it most for acuracy there. If you calibrate it running it will be off when walking. I'm kind of a data nut so I look at this a bunch and it stays accurate for me at my usual pace. The S3 stride sensor has no switch and the battery is now a coin cell. This is nice to me. Its also smaller than the previous sensor.
The GPS .
Polar G3 GPS Speed and Distance Sensor Set , an additional option, is more of a fun option for running and I'll use it this winter cross country skiing. The watch will use both the stride sensor and the GPS at the same time. This is something only the cx version has. If the stride sensor is on (you have to turn it on) the speed, distance, and cadence are all used from it and the GPS data is simply a record of where you went. When using the ProTrainer software you can look at your route in Google earth or a .gpx file viewer - I use Garmin's MapSource. The watch marks a waypoint when laps are set. I've used this to double check distances. I will be running in a city with lots of buildings in the near future so I'll see how well the GPS records there.
The unit does come with the polar usb irda port in the box which I find works well on my Windows XP laptop (Dell). Nothing I could find indicated it was in the box.
The software is very similar to the prior versions to me. The one thing that is a bit wacky is the way the watch settings load. I have an email in to Polar about this. I find I have to be careful when updating the settings via the irda interface as all the settings from the watch are not always loaded when the watch data is read. When you write any of the settings they all get written so this can erase or change settings. So, I have to check all the screens and make sure my data is the way I like before hitting save. I hope this gets fixed. The other wacky thing is the mileage in the exercise dialog is not the same as the recorded mileage from a run. In my software it is always a few miles higher. I just type in the real mileage. Have an email in on this as well.
Overall I really like this Polar watch. I give it four stars because of the bugs in the software