Jelco Easy VTA on the Fly

@lewm in fairness, it's something that is useful and an extremely niche, enthusiast product. 
@gary7  these are cheap knock-offs of the OP's product, which looks and apparently is a more highly engineered device.

Some more nice pictures of the new Improved version.

https://www.analog-forum.de/wbboard/index.php?thread/134608-jelco-easy-vta-on-the-fly/&pageNo=22

This is a very interesting product.  Would it fit on a Pro-Ject tonearm mount? Cheers,

Hello

If the Jelco has a 18mm shaft, then it will fit just fine.

In the meantime, nice review from The Ear Magazine.

http://www.the-ear.net/features/vta-made-easy

I don't really change carts that often. Would this give better value than the ammonite collar or is it advisable you have both?