Here you go.
Product - Polar F6
This one has alot of features but it also costs alot more than the ones you linked to. Aside from monitoring heart rate it also tracks calories burned which is very useful.
To answer Texmo's question. Heart rate monitors give you additional information regarding how your training is progressing. You can find out your max heart rate, find out how much you can recover between rounds in a fight or between exercise circuits. You can test you resting heart rate. Very useful to find out if you're overtraining, since the HR monitor will give you a higher resting heart rate than normal. Some can count calories. Its just another tool but a very useful one for trainers and athletes who like to know how thier body is responding to training.