Picked up a Retrotink 5X scaler that works quite well on my 4K TV.
Even though the name is 5X, it goes beyond 5 times for 240p. if your TV supports it (up to 1440p).
Cleans up composite well
Accepts Component, S-Video, Composite, and Scart (not JP-21)
Scart port can double as an additional composite or S-video port with an adapter
$275
Restocks in June / July
Deinterlacing for those consoles that output 480i, which is said to be better than bob and weave techniques
Switches resolutions without dropping signal (I.e. games that have different resolutions for gameplay vs menus)
https://www.retrotink.com/product-page/5x-pro
That said, I still prefer using a CRT, however that is just a preference. Been using it for FC twin over composite at 1440p and it looks really good.
ECU Professor has been posting pictures, you can scroll through their timeline, if you want to see what the results are compared to other devices.