I love the RG35XX and Mini Plus, and all other lower-powered handhelds. Those are the ones that will never stop being relevant. The ones that stay squarely in their lane and do specific things really well. It's the high-powered stuff that will get outdated!
I just recently purchased an RG35XX and I'm absolutely in love with the device. It's literally my favorite thing ever. I love how I can also play new homebrew games on it too and support indie devs. Also the Garlic OS is amazing and I've customized my theme into a cute Kirby Super Star one. I enjoy these video game generations the most and love being able to quickly and easily swap between systems and games. I find the system light and comfy. I loved it so much I gifted one to my friend also. I REALLY LOVE my RG35XX. The new one looks great too but I'm more than happy with the og. Don't think I'll be upgrading any time soon.
I'm still pretty happy with my original RG35xx I got for ~$50 or so If I didn't have the original I'd be tempted to get the RG35xx plus since being able to play some psp titles would be tempting and wifi is also very tempting. But all in all, I got the clear atomic purple and I don't really need more than one retro handheld so the OG is still working well for all my retro needs when I don't wanna lug around my steam deck.
How does any device become "not relevant" is the real question. At this point, nothing should be relevant with the steam deck being able to emulate literally anything that you need
