My husband got me a Polar for christmas. It is the very base model. I had to fuss with the monitor the first few times to figure out how I best liked it, but now it is quick and easy to hook up. There are some things to keep in mind with it. The pads have to be SOAKED in order to work. My mare rarely sweats that much and if they are not soaked in the beginning they won't work very well. The sensor on the montior strap and the watch you wear have to be fairly close or it seems to lose the signal. Once I figured out how to attach it to the d ring of my english saddle up by the pommel, it hasn't given me a problem. This one also has GPS, but it is a different piece and you have to clip it to your belt or to the saddle pad. Not a big deal, but is something else to worry about breaking. I think the more expensive models have it built into the watch. I do like having the HRM and GPS all on the same watch and the controls are super easy. It will display distance, pace, HR and time all at once and is easy to read. It doesn't connect to your computer at all. Again, that is in the more expensive models.
All in all, I have been happy with it. He wasn't sure if I would use it and didn't want to spend a lot of money and it be wasted so he just got the entry level model. If you think you will use it a lot I would recommend looking into the higher levels for ease of use. One last thing - the endurance rides around me require you to take all tack off at the vet in and end of race. With this set up you would lose the HRM when taking off the tack since it attaches to the girth.