The absolute beauty of cluster sets is that you can do 4 - 15 reps at or above 90 % of your training max. (blog.trainheroic.com)
If muscle mass gain is not an option pay close attention to diet, this will ensure limited gains in size and still leave room for neural adaptations while training with cluster sets. (strengthsensei.com)
To make it more brutal, set a timer for 5 minutes and perform as many cluster sets as possible, dropping the number of reps per set when necessary. (fitnessandpower.com)