The only benefits of the Ultra over the cheaper Series 9 are slightly more battery confidence (you'll still charge it daily), a couple of exclusive watch faces and a nicer included strap. It also looks different; the jury is out on whether it is better.
If its gym and fitness you'll find the Series 9 or SE does 95% of the exact same job for a lot less cash. They're
brilliant!
If he is someone who is hiking and out in the mountains for a few days at a time the Ultra's battery will not last that long, despite Apple's clever marketing telling you otherwise. For that (and even deeper fitness tracking) the
Garmin Fenix will give you 2-3 weeks of comfortable battery life. It works 100% with the iPhone.