They're also relatively big fish, and get relatively boisterous, rather than aggressive. They make good shoalers with the more aggressive focus fish or act well as a primary school themselves, but I'd be concerned about them with something as small as a guppy, particularly on their own. I have 7 of them and they do school relatively well.
I have kept them and a straight answer would be no as they will chase the guppy's and nip there fins and they will get too big. Also they may eat your guppy and platy fry