I have the Size Matters pump, and I do like it. Just be careful, sometimes the pump gets stuck a little, so don't try to force it too much when that happens (I imagine that's how people end up breaking them).
UNFORTUNATELY, my largest cylinder doesn't have a tight seal like the smaller two. The smaller ones, I could pump, detach the pump, and do things around my house while I left it on. This one, however, loses all suction as soon as I detach it, and even with the pump attached, it slowly loses suction while it's on. Because of this, I'm forced to lock myself in my room for 30-40 minutes twice a day, I can't move from my bed, and I have to keep an eye on the pump and occasionally have to re-pump. I'm going to try e-mailing the company about it, but I'm not sure they're going to care enough to send me a new cylinder.
Also, don't listen to people who say pumping doesn't do anything. They have either never pumped before, didn't do it properly, or didn't do it religiously enough to reap the benefits. This pump has helped me get the most out of the growth I'm getting from starting on T, as well as when I use it long enough, my guy stays more plump throughout the entire day. I don't pack, so it's really great feeling it able to stick out and rub against my underwear. I feel like I'm actually making progress, and can feel the results of my commitment throughout the entire day. It's great.
Most people who pump seem to suggest only 2 15-minute sessions each day. I'm not really sure why. It's a good plan for starting off, but personally, I try to go for at least 2 30-minute sessions a day, and have gotten better results from recently bumping it up to 45 minute sessions. I just make sure not to pump too hard and keep it comfortable. If you're smart and safe about it, there's no reason not to try for longer.
For reference, I'm 2 1/2 months on T, my guy was almost non-existent when I started, and I'm already able to use toys for masturbation, without the need to even pump beforehand.