it is an Android modified by Samsung
only Samsung and Apple phone is easily bought here, Xiaomi, Asus, Oppo are also available but it is less common
first it is bloated, full of apps and features that you don't need like, upday, flipboard, linkedin, word, ant, ar apps, bixby, link sharing, wifi direct which don't work with other Android
and it also sends lots of automatic request, from dqa, diagmonagent, and other samsung apps(including homescreen)
there are also report by appledaily that if you are at certain region like hong kong, all your DNS request are rerouted to 114, congent
you can, you need adb and command like this "adb shell pm disable-user --user 0 com.samsung.android.dqagent"
no, com.sec.ims will cause bootloop, com.samsung.android.app.telephonyui will cause you not able to change mobile network.