I used to run a shop where our panel saw was an Altendorf F45 Elmo. I had a digital mitre gauge for that which read in increments of 0.1 degrees, which if you remembered to note down things was really repeatable. Downside of a saw like that was the mitre fence alone cost about twice what that Hammer does (new) - that and the enormous amount of space such a saw requires (about 600 or so square feet of floor space to be able to use it effectively)
Yup, they are top bits of kit, we have an F45 down at the boat yard in Spain, not that I have much use for such a beast myself. In that class, yeah, I'd expect reasonably accurate mitres and the gauge to be spot on. But to calibrate it, you'd need what...call it £5k worth of reference angles and other lab grade equipment to have it really perform 100%. I suspect he'd need an even larger set of wheels than for the Hammer, too. lol
As for me personally, I tend to look to the japanese artisans for joinery knowledge such as this, because their mitres are absolute perfection, and done with hand tools. There is this common misconception amongst relative beginners or even intermediates, that you must have the latest and greatest power tool to do good work, but it's simply not true. I'd say personally, that you need as much skill to set up a perfect mitre on an Altendorf, as you do to do one by hand as the Japanese do, it's just that the skill set is different.
Perfection in furniture joinery is incredibly difficult. I've been at it for many years and only now am I starting to get it to the point where my joinery is truly to fine furniture standard and it's still hit and miss on occasion, but thats part of the fun.
Back to the OP's conundrum. I'd love to tell him to get a Kapex, because it's probably the best mitre saw you can buy. But I cant help feeling that for the same money, he could get a couple of decent engineers squares/angles, a quality hand saw like a Disston, make himself a mitre box and then buy a lie nielsen 62 or whatever to finish the ends. Ah well, I suppose that involves a ton of skills too in various areas.
No simple answer to this question, but maybe I'm just nitpicking. Hard to know what someone else feels is acceptable to them. I guess it's just important to acknowledge that whatever you want to do in woodworking, there is a learning curve and no real shortcuts to producing quality work.