There is a bit of a problem with hammer strength machines if you are looking at the way they produce a force curve. If you are using free weights the force curve (the way in which you generate force) starts low then progreses upwards and then tapers off towards the end. On a hammer strength machine the forc e curve starts low and prgresess upwards until and at the end of the motion it is at its highest peak alowing for a peak contraction. There is a slight problem with this if it is used to often. Lets compare a barbell bench press ti the hammer strength bench machine:
In a bb bench press you unrack the weight and lower it down to your chest to begin the lift. From there you push straight upwards, begin generating force, then as your upper arms become parallel to the ground to are generating your most force since you are at the greasted disadvantage against gravity because the lever arm (you upper arm) is at its longest length. Once you get past this point (which is a common sticking point) you are then home free. Your force starts to decrease because you are coming to the end range of motion and your rear delts, lats and rhomboids begin to fire in order to slow the bar down to end the lift.
On a hammer strength bench machine you are begining the lift by pushing out (similiar to a bench press) except the way they rae built and the way the force curve works is a bit different. Now at the begining of the motion it is easiest to push and as you push further it starts to get harder and harder for you to generate force until the end of the range of motion where it is at the hardest and most difficult for you to generate force. The great thing about this is that you can really force a good contraction making this good for hypertrophy. The bad thing about this is that if you use this machine all the time your brain begins to formulate a general motor pattern saying that it is okay to generate maximal force at the end range of motion during shoulder flexion, or in this case horizontal flexion. If your brain does that then you may actually end up hurting yourself or pulling a muscle doing something in everyday life (like pushing someone or something) and instead of your lats, rear delts adn rhomboids firing at the end range of motion to slow you down (a proper motor pattern progression) you may hyperextend and pull something.
So my point (and a long one at that....sorry) is use hammer strength in moderation.
I think I can only put like 15lbs on each side but I can press 30lb DB's 
