You could make the argument either way about how good bow flex is for workouts. They're fairly inexpensive and do provide reasonable resistance training. I have an Extreme 2 and bought it with the standard 210 weight kit. Upgraded to the 310 pound kit and that was simple. You just plug the two new rods into the already there holes. Now I am upgrading to the 410 pound kit. The box it shipped in was kinda beat up but the kit wasn't damaged. Installing isn't as easy as just sliding the bracket onto the one already there. There's two screws that have to come out the bottom of the rod holder. A new bracket goes on the bottom and new screws go in holding the new 410 kit in place. This all has to be done blind with a stubby Phillips screw driver. So all that being said ya they add another 100 pounds of weight so they do what they're advertised to do. Four stars because they need to make the machine able to accept this weight upgrade much easier.