I think also check out just once where @brendanhousler demonstrates the device on his youtube channel (one of the most underrated cycling channels) and you’ll get an inkling of what he means. That device doesn’t have you just doing some yoga breathing or deep breathing exercises. It’s a real workout & it forces hypertrophy in the inspiratory muscles. And I’m not just saying that because I have some intellectual capital tied up in inspiratory training…I’ve actually seen the before/after images so in that respect improvements are tangible.
Does increased inspiratory musculature result in improved rowing/repeated sprint/cycling performance among trained athletes? The answer to that question is a lot more mixed. Sometimes yes, sometimes no. But seems like it’s never a negative impact, so why not? But not as your primary training focus. Train first…the evidence that training intervention helps is overwhelming & incontrovertible. Drop weight 2nd…the evidence that lighter bike/rider goes up hill faster is incontrovertible (on this forum we obey the physical laws of the universe!).
After those houses are in order, if you want to do some inspiratory training go for it.