EF Teleconverters on R mount cameras-restrictions?

[olyduck]

Hi-I anticipate buying an R mount Canon in the near future and I'm trying to decide whether I also want to trade in my

EF 100-400 L (first generation).  My question is this:

If I use a Canon 1.4 or 2.0 EF teleconverter with the EF 100-400, on an R mount camera (with adapter of course), what restrictions to auto focus or other functions might I encounter?  Would those same restrictions also apply to an RF 100-500 with an RF teleconverter?

I mainly ask because, despite the great reviews for the RF 100-500, it also costs a big chunk of change. If I could retain reasonable functionality with my EF 100-400 with EF teleconverter, that would help.  On the other hand, if that combo would prohibit some of the cool functionality that an R6 (for instance) offers (like eye focus, etc.), I might spring for the RF 100-500.

Thanks for any feedback. 

[ebiggs1]

"... the RF teleconverters a significant  step up in image quality over their EF predecessors."

Perhaps so, but I will never know since I have no inclination to try or much less buy one.  Even if they were great IQ wise they are still another "thing" you have to deal with.  That is my biggest objection to adapters and/or a tel-con.

I have six tel-cons so it is not like I have never been exposed to using them.  In the beginning I did use them quite a bit. I found out I didn't like using them so they sit on a shelf in the formerly stop bath stained walls of my ole darkroom.

As far as adapters I have a boat load of them. They are all mostly junk.  The one exception is the Ed Mika FD-EF adapter.  It works well. I have one mounted on my FD 500mm f8 cat lens. I enjoy playing around with it.

BTW, I do not have any III versions so I have no comment on their IQ ability.