Should you open up about your ex on a first date?

We're a little puzzled by this one.

We thought that one of the cardinal rules of dating is to not discuss an ex on a first date. Because tbh, if a lad started chatting about his ex when things are only heating up, I'd be a bit worried he's still into her. Wouldn't you? Well, this expert claims that talking about exes on first dates is all well and good. In fact, we should do it. Relationship expert, James Preece, believes that while most people talking about an ex to a new love interest is a bad sign - he thinks the opposite. He believes it means they ARE over them. Speaking to the Independent, James said: “If you can joke about the situation, it's a clear sign you are ready to move on.” Dating psychologist Madeleine Mason agrees, saying that: “There is no harm in swapping stories and if the relationships have been significant; the experiences from there can be valuable in getting to know someone." She also notes that if a potential partner doesn't like you talking about, it could be a warning sign. “If your date is jealous of you simply having a healthy relationship history, it’s a red flag which is better to see sooner rather than later." Would you talk about an ex on a first date?