Variable InfraRed Filter? Is It Worth It?

While I was exploring the various tools nd accessories that make infrared photography possible, I found a variable density IR filter for a reasonably low price on an e-commerce site.

Is it a good buy? Is it worth using?

The thickness of the filter itself causes it to vignette strongly. On my 14-30mm/4, I can't zoom out any wider than 18mm or the filter is visible on the edges of the frame. The cross pattern or unevenness you get in skies with polarizer or variable neutral density filter is even stronger with this one.
Build quality is poor with the glass easily sliding around inside the metal frame. While testing it, oil began to leak out of the filter onto my fingers. What if that oil had gotten onto my lens' front element? That's not a risk I want to take.

http://kyleclements.com ... https://www.youtube.com/watch?v=aXY-uX96JIY