I used to use them from time to time about 35 lbs ago, and as other suggested, ride them in a doorway to help you get started. You measure roller training by how long you stay on them, not how far or fast you go - it's hard to ride them slowly. I think I got up to 25 minutes once, and was depleted. It takes great concentration to stay on them, but when you hit the open rode you'll be amazed at the straight line you can take - you can stay on the white line on the edge of the rode for much longer.
Dang, now I'm thinking of getting a set again...
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If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.