For me he's the signing of the season , even more than Alli or Alderweireld because its players like him that we need to look for. Skilled, experience, relatively young and on the verge of a real breakthrough (even if he was already pretty established before that). The kind of player we can just about pay and the richer teams just overlook. He can be a true gem, two footed, always dangerous, always motivated and just has that natural goalscoring ability.
It's tough to say there's a single standout "signing of the season". Don't get me wrong, Son adds some needed versatility and creativity moving forward but I think we cant neglect what Toby as done to our defensive woes. I'd say Alli and Son are on the same level of what they can bring for us in terms of attacking options.