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I've had a couple of Brother Ultraportables. One was a Kmart model that ranks as the worst typewriter I ever owned (and the first typewriter I ever actually owned).
I currently have one that needed some work (I fixed it up using parts from a broken Monkey Ward (also a Brother) and it's now very usable.
I would definitely recommend a Brother as an ultraportable too... although I'd be hesitant to try and write a novel on it. I think my Tippa or Skyriters (or perhaps a Hermes or Olympia - on my wishlist) would be better for an endeavor like that.
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I have a Groma Kolibri that is great for taking on the go. I also have an Oliver Portable 4 which travels well. I still love my Smith-Corona 5 series Sterling though. I find these very portable and sturdy.
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5-series Smith-Corona models are fantastic, but far too big to be considered an ultra-portable.