yeah. Spot on. For the app, I don't take into account the density, but racket head is taken into account. Prominent shapes are oval and isometric, so I have separate co-efficients for those, which were learned using regression.
One challenge that I haven't figured out yet is when 2 different types of strings are used. It seems, some advanced players use different strings at different tensions for the horizontal and vertical strings. Like 32x28lbs or other similar configurations.
if spokes come in standard guages, it should work for bikewheels as well. There may be some differences due to the bike rim material, but in case of badminton, I found out that frame material could be ignored safely.
I'm of the same opinion as you, and have infact built projects with zero signup requirement. racketmeter.com being one of them.
So, I understand your POV. But with an AI product like this, where every trial has a cost associated, people who are not compelled to signup, might not be a good fit. I'm certainly missing out on potential users, but being a bootstrapped founder, it's a call that I had to take.
But I do take your comment sincerely, and will try to think of creative ways to show people what it feels like to use the product and see the aha moment in first 20 seconds.