Fast point or grout for porcelain slabs outside?

[uptown47]

I've just been asked by my builder whether I want Fast Point or grout in-between the newly laid porcelain slabs (600x600x20) outside.

I asked about the differences and he said that Fast Point was easier to put in and so cheaper. He said that he'd enquired in the shop and Fast Point was fine for porcelain slabs and could be put in regardless of the weather.

The grout wasn't a bit more work to do (and therefore more expensive).

I'm unsure what to go for and my Googling has come up empty? Can someone help me make a decision on this? Does it even matter? Are they much of a muchness?

Thanks