I have one and I love it! I paid $700 for latest one and I've had 3 different Bowflexs around my house since 89' when the first proto types where being made by Shwin ( I honestly don't know if Shwinn still makes them or not) No, you won't build a body thats 150# to one thats 250# ever. Though you will out grow the rods fairly quickly. Meaning the position that you have to raise the hand grips to do even bench press is near impossible with the amount of weight that I can do 5 to 8 reps with, so large gains are difficult. You have to curl the weight and bring it up, almost the same as getting db weights up by yourself without being able to use momentum to throw the weight up into position because it of course is attached to the power rods. I do higher reps than what you would do to gain mass and I do ok, my body responds well to 10, 12 even 15 reps.
Leg workout was mentioned by MK and he's right the power bands on my Bowflex only go up to 310#. It does have a very effective squat set up with pulleys at the floor and a powder coated diamond plating to stand on but 310# is not near enough weight even for me let alone some of the guys on this board. Although you can do higher reps which I do. You can do single leg sled and that will kick you butt. It has leg ex. and curl set ups that work fine.
It also has a lat pull down set up that works great too. If you've been to the gym enough you know what movements you want to do and what you want to get out of it. The amount of room they take up is comparable to a free weight set up and you can always fold them up. With some ingenuity and proper form for the exercise your doing its IMHO not a bad investment if you don't pay full retail and shipping for it, their in the newspapers and buy ans sells every day.
I've been working out for over 20 yrs and have spent allot of money at a number of gyms and I had to drive to them every day. I still sometimes start going to the gym when I need a change just to keep it interesting and that always helps the motivation. What i do like about it is I listen to anything I want on the radio and I even have a small TV set up in the room if I want to watch it in between sets. It's even quiet when I want it to be, I never have to wait for any thing and I don't have to take to anyone if I don't feel like it.
Again JMHO