There is no doubt that the high tech measuring systems work. If they didn't people would not buy them and in turn they would be off the market. On the other hand, Juan is right as long as you have enough contact surface on the measuring sheave. There is actually a formula out there that tells you how much contact the wire must make with the circumference of the pulley.
So if you want to save money you can use the contact wheel. You can increase the accuracy of the contact wheel by using a pulley with a lot of teeth and a non-contact pick up sensor. If you use a single tooth then it takes one complete revolution to determine the footage. If you use a gear with 60 teeth, then each tooth is 1/60 of the circumference and your accuracy increases.