Haven't bought the Penimaster. Most guys seem to have issues with wearing it for as long as necessary because the noose at the end seems to cut off circulation. The wide band this device uses is more comfortable, but I've heard some users complain it is also difficult to wear for the same reason. There is a better end you can get, the suxtender, that uses a suction cup that fits over your glans to better distribute the tension and most men think that is superior if more work to take on and off.
I do have a jelq device but use it only occasionally when I'm feeling lazy. Your own hands are more accurate and provide better coverage and more easily gauge pressure than the device will. It is useful for when you're in a hurry and don't want to get lube all over your hands and it does what it says.
If you're thinking of starting PE, I'd advise you to do the three month newbie routine no matter what other methods you're thinking of trying. It will teach you how to jelq, get you into the routine, and, most of all, condition your penis for this kind of work. You'll learn what you can and cannot take. All men are a little different in what works for or is tolerable by one man may not be for another.
Just about every injury that occurs happens when someone jumps the gun and does something more advanced than they should or ignores the instructions. The first dictum is, "never overdo it." PE is safe when done within the guidelines. Many men have spent a long time working to make these exercises safe, sometimes at their own injury. Do not disregard their lessons. If they tell you to do or not do something, listen because you could fuck-up your dick fairly easily. Don't do that.