I use these a lot working as a physical therapist and also as a personal trainer. They are very versatile and easy to take with you on trips.
One of the things that is different about working with bands in comparison to weights is that the resistance to the motion gets greater as the band gets stretched farther. Lets say you are doing bicep curls with a 10 lb dumbell, it's always just 10 lbs. If you do a bicep curl with bands the resistance will be lighter as you start the exercise and will become much greater the farther you bend your elbow. You can use this feature to your advantage but it can also limit your ability to move through your full range of motion during an exercise. This isn't a negative, it's just different and something to be aware of.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS