will these adapters work well?

[nhodgkinson]

I have some Zeiss Contax and Nikon Ai/Ai-s lenses and need to chose one to build a set of primes for video to be mounted onto a Metabones Speedboster.
I really like my Zeiss C/Y lenses and and had set my heart on these so started to fill out the set then I realised that the Speed Booster is Nikon mount so the C/Y lenses would need to have an adapter with an element in it. Fotodiox make one and I guess it's of a high quality but I am concerned about this extras glass. Would the extra element affect the image?

Fotodiox Pro Lens Mount Adapter - Contax/Yashica (C/Y, CY) Lens to Nikon SLR/DSLR Camera with Glass Elements for Focus Correction - Pro - Full Frame / APS-C Body - Adapters

Otherwise I could just give up, save myself some money and go with the Nikon Ai-s range.
Dose anyone have any experience with the adapters with the elements in them? I have not used them before.

I found a mounting solution by Leitax that involves removing part of the rear of the lens and replacing it with a mount they sell. I believe the registry distance is not negative but only very small so they have come up with this mounting system you can fit. It's quite pricey, about £50 a pop so £25 more that the adapter with the element in it but maybe a better solution. It only works with some lens but it works with all the ones I would need. Anyone have any experience with this?

Zeiss Contax lens for Nikon cameras