Should every subversion of Android Lolipop (5.*) include an option to add multiple users?

I've purchased the tablet from a Serbian company called Tesla with android 5.1.1, and I've read that Lollipop includes that option by default. I was quite surprised and furious that this option is not available on Tesla's tablet even though its Android Lollipop and the icon is there where it should be, but it doesn't work. They did not mention that "minor flow" anywhere, and now the tablet is needless for my nature of business. They gave 0 f***s for my problem and told me that it is not their business to mention any of the Android 5.1.1 functions and options, even if they change something that should be there by default. If it turns out that by some legal obligations and bonds, the version of android they sell with their tablets is obligated to include that option, i would like to find a way to legally sue them. Thanks for help in advance.

Manufacturers can choose to leave that option out. I think my 2013 Moto X had it omitted, as does my Samsung tablet - both running 5.1.1.

Nope. You can't legally sue them, and that function of Android is not obligated to include that option. Android is open source, meaning anyone can get Android and alter it as they see fit for their own use, and this includes altering to sell their own Android devices.