I doubt that scales on all bandsaws are unlikely to be accurate. I accept the one on my N4400 is just a guideline.
I also have never used an aftermarket scale. I simply tension using the 1" mark as a rough estimate, and then go a little more until there is minimal blade deflection. I am on my second 1" Lenox Woodmaster CT. This one tensions more easily, as if the blade has more spring in it. The previous one struggled to get to the 1" mark. It is possible - a more likely explanation - that the new blade is slightly longer than the old one? In any event, the new one cuts more smoothly.
By the way, I re-sharpened the previous 1" CT about 5 times before it eventually gave up the ghost (diamond disk on a Dremel).
The Hammer N4400 is a good bandsaw, but I agree that it is an entry level for the Felder make. It has good power, but there are areas for improvement, which one pays for. I am happy with my three Hammer machines, having had good service from them and the agent, who is nearby. That was a big reason for going with Hammer.
With regard size of blade, my N4400 is about 9 or 10 years old now. Earlier models went to 3/4" (as the recommendation). I believe mine can go to 1 1/4".
Regards from Perth
Derek