Most people don't go to prison for a 25% sentence discount if they are advised they have reasonable chances of getting off completely.
He starts well when explaining the statutory text, loses a bit of credibility by treating CPS guidance as some kind of legal gospel (rather than a practical guide to what the prosecutors might decide to pursue, irrelevant by the time the case gets before a judge), but then just slides into unsupported assertions of opinion. He's pretty slick and persuasive on a surface level but no, I don't find him convincing. He literally distances himself from what he saying by stating it is just opinion and not advice - sensible of him, but when he says that, it is to be taken seriously.