This is also an advantage, as it has been shown that this is how our muscles evolved to work and is a natural type of stress to the body that helps us develop better stabilization strength, and power as well (Hatfield, p. For general population training this will improve a client’s joint integrity through training the stabilizer muscles and also teach them how to move objects in real life better than machines.
In sports training these types of technologies could be used to train power for sport, such as the example I gave of a martial artist using a resistance band to train his kick. These tools can also be used to help someone through sticking points like using resistance bands to do reverse barbell bench press, or assisted pull-ups, to help the athlete build strength through the weaker ranges of a movement.
But to reemphasize what Clint said, these days are taxing and no one can tell you exactly what percentage you need on the bar unless they're training with you or seeing all of you dynamic work. It should feel like it's accelerating the entire rep.