Don't buy a shitty vest and later complain about aforementioned shittyness. Buy a good vest or a dip belt depending on your training needs.
I have the 75 long + 25 short V-max weight vest. I also have 20-lb ea. All-Pro Ankle Weights. I purchased both of them November '06. The original idea was to train from the FDNY CPAT. Nowadays I train with them sparingly. When it gets very colder and I can train inconspicuous I'll do so. Read the last paragraph for some warnings.
For training cardio I have to recommended stairs, trail walking and hiking. Personally, I use a Polar F-6 Heart Rate monitor whenever I use my vest and ankle weights to accurately gage my cardio. Remember 6 mph at bodyweight is not equal to 6 mph + added weighted. I've never run more than 5 minutes with weights of any kind.
Sprinting is very risky. Once I did a chest plant (I fell/collapsed) because I couldn't decelerate properly and my legs just quit on me. By the way I never use the ankle weights for running or sprinting. Also, bear in mind that overtime the short vest will sag, this is only noticeable when your sprinting or doing other rapid movements.
Jumping Rope is surprisingly easy and effect with both the weight vest and the ankle weights.
Bodyweight training is excellent. Though I think a simple dip belt is generally more practical than a vest. Training will depend on your situation and whether you have spotters to place weights on your back for weighted push-ups for example.
As far as the proper progression, I wouldn't recommend starting out with more than 10-20 lbs. I started with 50-lbs for stairs and it was killer. However, progress was quick and within a few months I was up to 100-lbs. Later on the ankle weights were added.
Looking ahead getting the 150-lbs (75+75) V-max vest and a pair of FiveFingers looks promising. I would use the combination for cardio mostly and do sprints from scratch (bodyweight) to an additional 150-lbs (eventually).
Other notes. Initially breathing was very laboring because of the load the vest placed on my chest. Now I breather deeper and with more force with or without the vest. Coming back to weight vest training is very easy even after a long break.The 40-lbs of ankle weights is significantly more challenging than the 100-lbs vest.
If you train in public, expect to be questioned by detectives and possible house visit(s) from homeland security. I live in nyc and whenever I do calisthenics with the vest at the park I get asked the same dumbass questions from people whether or not they know me and whether or not they are law enforcement. I wouldn't recommended wearing an mp3 player, maybe just a bluetooth for your cell. Wires look conspicuous and in the U.S. they may shoot first and ask questions later. Seriously.