Jelco Easy VTA on the Fly

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? 

You can't have both. The EasyVTA includes a special base which apparently has "tighter tolerances" than the standard Jelco collar. No idea how it compares to the Ammonite base. (I have 2)
If you want er, easy VTA, this is the best way to do it. 

Very nice and detailed review.

http://v2.stereotimes.com/post/tweaks-for-geeks/

...just a bit of a caution.....as you raise the rear end of the arm, you are decreasing the vtf.  ...not so easy to listen/adjust/listen/ajust, etc.