There are basically four different makes of helicoids readily available on eBay. They are: the generic ones that I bought and bad quality; one from Hawk Factory in Taiwan, which has good reviews, but at about $130; one sold by Fotodiox at $120, and the other, which I bought and I am reviewing, is a Yeenon 18-33mm, at $57 (free shipping if you offer to pay the asking price on eBay). I chose the M42/52mm version, so that I can use it on NEX, Micro 4/3, and Canon EOS through the M42 adapter.
The Yeenon helicoid took exactly one month to arrive from China. It came with a (relatively) nice box, and even a guarantee. I could feel the difference in built quality as soon as I held it in my hand. Much better than the generic ones I bought. The Yeenon is slightly larger in diameter. This has a negative effect on the NEX-5N, as the focusing ring touches my middle finger that grips the camera, while focusing. Also, there is still a very slight play between the focusing and the mount, just enough to feel it. It's not a big deal, but nevertheless lessens the joy of using it. The focusing is relatively smooth, but a bit too much resistance. I am sure with use, it will loosen up.
So far I have only used it for a week, but I enjoy it much more than the ones I had before. It's not as good as the Vivitar 2X focusing helicoid, but very close. I just hope that the build quality will hold up and last more than a few months.
The Yeenon 18-33mm helicoid. Click for larger
Face Off - Left Yeenon 18-33mm; right generic 12-17mm. Click for larger
Side by side. Click for larger
Intense colours - NEX-5N & Schneider-Kreuznach Componon-S 80mm f4. Click for larger.
Symphony of colours - NEX-5N & Schneider-Kreuznach Componon-S 80mm f4 @ f5.6