I've been using Plex Media Server since 2016/2017 as my main media solution, I cut the cable and stopped paying for subscription services because the outgoings per a month were ridiculous for the content I was getting. I have it installed on an old QNAP that I was given from my uncle, with 16TB of storage in it - granted, one of the drives are failing and I haven't replaced it yet, but I digress.
I used to use XMBC (Kodi if you're young) before Plex Media Server, and it done me well for a long time on my Xbox Classic but times moved on, updates became less common and it was time to move on. The major difference between XBMC and Plex for me is that I can watch movies literally anywhere in the world on any device as long as it has an internet connection, an app store or a web browser, and a country that it's not blocked in - this is what made it such an easy decision to move.
My single, only gripe with Plex vs. XBMC is that Plex has a monthly subscription cost to do basically anything other than watch movies on your laptop, using it on other devices such as your phone and in some cases smart TV's, requires a subscription. Now, the subscription isn't all that expensive but it does seem kind of ironic to pay to watch movies and tv shows you illegally downloaded off of some dodgy torrent website hosted in Russia. It has two subscription offers, monthly and yearly, and lifetime - the lifetime one being a one-off-payment of £94.99, monthly being £3.99 or £31.99 for yearly - a few years ago, around 2016/17 Lifetime used to be half the cost, however they increased the price and never really warned anyone, the annoyance in this is that if you can't afford a £94.99 outright payment you're stuck with one of the subscription options which isn't great, because then you have a recurring monthly or annual cost to watch content you didn't even pay for.
Plex is great, and it has some amazing features and the company behind it deserve some form of payment for the work they put in between the server app, the phone apps and the fact they've somehow managed to get it on everything from your iPhone to a Samsung Fridge running Android - it's everywhere. My only request is, maybe if people have been paying for it for 4 years give them a discount code?