To keep it simple:
You get little to no negative resistance which size building heavily depends upon.
If you want to burn calories, get some cardio, and just get some regular exercise, then it might be a decent buy.
If you want to progress and grow muscle, then this is not a worthwhile buy.
To explain it a little deeper I'd like to address the following myth:
"Dude, I don't want to get big and 'roided. I just want to stay cut".
This is nonsense because you don't get "big and 'roided" without steroids. This should never be anyone's concern because the average
human being can't naturally look like Ronnie Coleman. Of course, there are exceptions, but very
few. I guarantee you that those Bowflex models have done a cycle or two of steroids coupled with T3 and clenbuterol/albuterol.
Most people will "stay cut" by doing a strength and size building routine with a proper diet. You won't "stay cut" without building muscle. When you're lifting weights there comes a point that your muscles get used to what you're doing and without progress you won't achieve homeostasis, but will, instead, go catabolic and even shrink.
Your goal should be to get bigger and stronger. To be worried about getting "too big" is ridiculous. You won't get any bigger than you were already genetically predispositioned to without the addition of Steroids and/or HGH.
Personally, I'd get a gym membership, start playing soccer with friends on a weekly basis, etc. Establish things like this as routine and I PROMISE you, you'll get the results you want and save a load of cash you can spend on more guitars
If you really need home equipment, then invest in a cage with a smith press, etc. Those can be had for cheap these days.