Actually, they have the Nothing CMF phone, which is an absolute banger for the bucks!
https://murena.com/shop/smartphones/brand-new/murena-cmf-phone-1/
I wouldn't buy theirs. Rather get a second hand refurbished one, from the 222 supported models: https://e.foundation/get-e-os/
Discussion
Nice, i like the design of Nothing phone. But i'll check again if i can get the deal on the Pixel 8 pro for 349€ i don't think there is a better new phone at this price, it's almost x2 faster in performance than the CMF and have better cameras
I see on some reviews budget and mid Nothing phone are already slow and buggy at release, so it's not a good sign for the coming years, i like to keep the same phone for at least 3 years.
Maybe this OS make it better, it is lighter right ? What about the security updates on this alternative OS like this one or GrapheneOS ?
Upgrades come frequently, for both community builds and official. Here you can see the time stamps for the nothing builds: https://images.ecloud.global/official/tetris/
The best thing to do, is to do what you are comfortable with. I wouldn't pay too much attention to strangers online like me, but then again I would also never trust gogole to be even close to powerless over their own devices under any conditions.
Assess your threat model, weigh it against what you are ready to invest in terms of time and energy. You are already asking very good questions, so you are definitely on a good path from my pov.
Best of luck!