Help me confirm that Quickcast is actually allowed in LCS to a Friend

Ok so I'm trying to help a friend on his game and suggested him to try quickcast. The problem is that he feels that quickcast is cheap or is unskilled because he believes that it's not allowed in the LCS and that other pro players say the same thing or so he was told. I wanna help improve his game but it seems I need to proof to him that it is allowed somehow. .

I know this is silly but can I get a riot to confirm it for him since there's no official stuff about quickcast that I see.