Oh yes, I love my Galaxy S4 i9505!
The Samsung phone was introduce in 2013 and I was looking for a good phone to replace the S2 (which I purchase back in 2011, or was it 2012?) that was slow and a bit too hot to touch some times.
But then S4 came around the corner in 2013. I was amazed by the screen size, 5 inches! The 2GB of ram, the 13MP camera, and the latest Android. As long it had micro SD card reader, the S4 phone was going to be my next phone.
However, the model that I purchase was SGH-M919 and not the GT-I9500 (the international and unlocked version). Anyway, as it was a S4 it's good to go!
Then later, I broke the phone, purchase a new phone from eBay: SGH-i337 and unlocked it to use the T-Mobile sim card.
Then in 2016...ish, I wanted a new phone. The criteria were that it could not be bigger than 69.8 x 136.6 x 8mm millimeters, because I used my phone's mp3 player at the gym or running. Anything bigger would make me angsty. Also, I wanted a 5-inch screen with 1080p. Micro SD card reader was important also.
THERE WAS NOTHING!
From 2016 and onwards, phones were getting bigger and I was left on the cold. I believe the S4 is the best phone when it comes to screen size and dimensions. I wanted to buy a new phone that has the latest Android (Marshmallow in late 2015 and early 2016).
A lucky break came when I learned about custom roms, Rooting, and custom recovery for S4 phones from XDA web site. So I purchase a new phone, the S4 Gt-i9505 model and installed custom roms. There was CyanogenMod, AOKP, Slim Bean, and many other custom Android OSes. I love how you can have the latest Android's features in an old hardware system. The downside is that some roms are buggy and support only exist in the XDA forums. Nevertheless, the tradeoff was worth it.
"(8.1)Optimized LineageOS 15.1 builds version 3" is the one I am using for my S4. I like it, but there was a bug that did not let me made the calls. So, I have to reinstall the rom. Another problem is that that some roms are not compatible with certain hardware. Lastly, you need to have patience, skill, and time in your hands to experiment what roms are best for you.
The reason I posted this is that I love how you can squeeze some life from old hardware. Another reason is that if want to test your app in a different Android environment and not use the Android Studio's Emulator, then this is a good choice. I love how you can use Android's latest features. For example, I love how you can block some apps from accessing the internet.
I know this post is not about how to root, Android 5.0.1 to 8.1, or change firmwares, but it was the benefits of having options for your old hardware. Maybe another post I will post how to root your i9505 and and have Android Oreo on your S4.