Thoughts on this knight sac in the Anglo-Grunfeld?

It's not a particularly common line, but I run into it from time to time since I try to move-order my way out of playing against the Grunfeld. Anyway I know Black usually equalises with ...f6 and ...e5, but I found this idea (8. Bf4!?) in a game against Play Magnus age 11. I ended up accepting a threefold repetition after a long endgame struggle, but by my standards that's not bad so the sac can't be losing on the spot at least. Can't find this position in my database so was wondering what people's thoughts were on it.

Basically here are my thoughts, such as they are:

Pros:

White gets 3 pawns for the piece

Gets a protected passer on e4, and a queenside majority (so a possible endgame advantage)

Controls the centre without a decent way for Black to undermine it

Slight lead in development, and may be able to get rooks on the d-file before Black

Cons:

White's down a piece

If Black can force White to exchange a bishop for his knight, Black's bishop pair really comes to life

In some lines (where White plays f3) Black could get a minority-attack-like idea going with g5-g4, as fxg4 isolates the e-pawn and gxf3 gxf3 gives White a weakness on the f-file.

(Fritz thinks it's =, verging on =/+)

WHAT GAMBIT IS THIS

White might draw with some luck, but this is hardly an advertisement of this.