A steam deck can replace a huge number of devices, works very well, and I recommend it to people who don't need the latest console or superior gaming rig. I think that if you also usually have a laptop, it makes more financial sense to get a steam deck and thin, dedicated GPU-less laptop rather than a laptop with a dedicated gpu.

It is also just a good deal in general, hardware-wise and performance-wise. It has a very performant GPU, outperforming more expensive similar devices. It also benefits from being a consistent platform, like a console, so there are games that work very well specifically on a deck. You can also find user guidrs for making games run well specifically on a deck.

Also it is great for emulation.

So while it depends on personal finances and what you expect to get out of it, I think I it has a great balance between cost and what you get.