They are not limitations, this is the only way how this add-on may work. It's very heavy by nature, that's why it's not recommended by miniBB team for medium-to-large forums. It's created only for people which prefer habits to learning.
Different computers/browsers show different results...
Of course, Cookie are stored on the client side, and if you're on different computers, they are different clients and results depend on which time you've entered the forum and what topics where presented at this moment on the front page.
The addon adds a lot of data to the database. It stores data from all users (what they have read and not read), even if they only register and visit the forum once.
Of course, as soon as a registered user is logged in, the add-on will generate kind of cache for him. Despite it uses as compact database structure as possible, of course it will generate a lot of data that way.
As I mentioned above, we have "Checker
" add-on which does the job much more better, comfortable and efficient than the "regular" algorithm (invented by who