Sorry I forgot to ask just for final clarification does the latest version of NIK Silver FX co exist with previous version or does it override it that is the most crucial thing for me because the last version works very well for me and i dont want to get any nasty surprises
Thanks again
Constie
Let me come back here to continue.
Having used the tools since 
just yesterday I installed Nik 6.4 …
With Nik 4 the former versions were overwritten, while I could reinstall them as described …
The folder …\Nik Collection
still contains the installations of Nik 5 ( + 3 ).
.
So far, I’ve only installed Nik 6 ( by default in a separate folder ),
which then showed up in PL6 like this …
( Nik 6 – but as before it should be no problem to re-install the older ones )
.
and in Affinity Photo 2.2.0 …
.
like this
( Nik 6 )
.
and this
( Nik 5 + 3 )
note – some restrictions w/ Perspective and HDR
BTW, when I checked in Color Efex and Silver Efex, my former presets look to have been automatically imported.
And as @platypus mentioned, “use the trial time wisely.”