I can put my hand on my heart and say I do not know any
theory at all about the Grunfeld.
I know the spirit of the opening (attack and undermine d4)
and that is all.
I can recall one note from Euwe saying the white fianchetto is harmless
against the Grunfeld.
So after 5.g3 I played 5...d5 and laid into the d-pawn.
I then went for traps and I think if White does not play 17.Ka4 then
all I have is a good position, nothing more.
Once I found the Rook lift 19...Rd6 I knew I was going to pick up
a piece. (I love Rook lifts).
I then skittled through the game and towards the end I missed a mate
(22...Be6+) seeing only winning the unprotected piece.
No excuse for that.
If I was a 1.d4 player i would play an anti-Grunfeld line. It's easy
for Black to find the moves once you know the theme of the opening.
I'd play the Grunfeld more often but I love the KID & Benoni/Benko.
You will have fun with the Budpest, if you get to play it.
"1.d4 2.Nf3 is the antidote to all gambits." - Kasparov.
The good news is you can then enter a KID without worrying about
any of the f3 or f4 variations.