Mr. Surfacer as primer?

Saludos Amigos!
I was about to order some of Gunze's Mr. Surfacer from Rainbow Ten a
few minutes ago when I noticed that they also had something called Mr.
Base, which I presume is a primer (or undercoat if you like.) This got
me thinking ...
Now, although I've never tried it before, I'm aware of Mr. Surfacer's
intended use as a liquid putty -- used for filling those itty-bitty
scratches, seams, etc., where regular putty won't go without a good
dash of liquid glue, and this was also the chief reason why I was
thinking of buying it.
But ... Seeing as I'm out of Citadel Colour Undercoat, I was wondering
what you guys think of using it as a primer for Gunze's Mr. Color line
of paint? (I seem to recall some people mentioning that they've used
it a such.) It it something you would recommend?
And how about Mr. Base? Is it a primer? And if so: Is it any good?
TIA