After 11 exercises with training band resistance, I feel I can make a reasonable assessment of its value and utility. Even though I currently use the body, my general observation might apply to all types of this equipment.
Resistance band training does have limitations. First and foremost is the effect of "rubber bands". When you extend the movement, "resistance" increases. It was great. Not too good is the opposite effect. When you return to the initial position, the resistance goes to zero, in some cases. You can buy best gym resistance bands from various online stores.
Let's take the squat. In the bottom position with a free weight, you are still under the weight whatever you started. With resistance ribbon, the resistance becomes zero when the band returns to the "normal" length. Therefore in the bottom position, there is no pressure on the foot, unlike free squatting. The same thing applies if you do a line with the band.
It doesn't always happen, like by pressing the chest; you can stand far enough from the door to get the initial stretch for the initial position. However, I believe in most cases, when the bands are closest to a natural position; Resistance is very minimal.
Case In Point, when you move through a bow on the chest Flyes, I believe there is a point where the bands don't increase anymore. Therefore there is no stress through the movement section. With gravity that works on Dumbbell, it will never happen.
But regardless of limitations, there is no other conclusion than that this is a legitimate power building equipment. The advantage of this system in many ways is far superior to what can be obtained by the system of free weight for the home gym.