I wouldn’t trust any add-ons. I have the Bowflex SelectTech, but they’re expensive. That difference in weight is negligible. It’s not how much you lift, it’s how you lift it. Practice good form, flex the hell out of the target muscle, don’t just go through the motions. Never bounce the weight or use momentum to pull a weight. There should be a slight pause in the rest position. Count 1 second up, contract as hard as possible, and do a controlled 3 second count for the down. Then tell me you don’t feel it. If you didn’t, you’re not doing it right. Good luck.