Reddit mentions of Blu-Ray Player Laptop External USB DVD RW Burner Drive

No, the USB blu-ray drive plugs into your laptop. I bought one of these a few years ago, which is what I use to rip blu-rays and dvds. Ripping blu-rays is an entirely different realm though, because they're locked down a lot tighter with various kinds of encryption.

Bluray is just standard 1080p HD video. It's far sharper than what you get on DVD, which is standard definition 480p/480i. 4k is 2160p which looks even sharper, though I've heard the difference isn't very noticeable at a distance. Some 4k movies may just even be upscaled 1080p, so the extra resolution becomes redundant. The real gain that people find in 4k is the HDR colors (If it's supported) which can make scenes look more vibrant. 4kUHD is essentially the same as 4K as far as I understand; it's just another title for 4k.

Another thing about 4k is that you will need the right equipment. You'll need a 4k TV/Monitor (preferably HDR supported), a 4k supported devices (i.e. 4k bluray player, apple TV 4k, XBox One S, etc.) and a HDMI cable that can support 4k content (usually provided with the 4k device or TV). If you don't have all 3 of these, then your content will look just like plain HD.

I wouldn't suggest trying to watch 4k bluray on a laptop as there is practically no support for all the three requirements I just listed. A standard DVD/CD drive can't play bluray, but you can use an external bluray drive to play content on your device.

I might not suggest getting 4k on desktop as that requires another round of effort and money (speaking from experience). The drive is pricey enough and it has even more specific requirements to get working.

TL;DR: 4K content is really only worth it if you already have the equipment, or plan to invest in it. I'd suggest simply getting the bluray if you really do want it. Otherwise if money is that much of a concern, then maybe just go digital as the quality is better than DVD.