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.

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.

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 btw?..).

Great Paul. Thanks for the explanation. Although I'm very new to MiniBB, I'm definitely in love with it now. ;-)

Please write a step by step how to do it to show unread topics

There are no steps. Topics you haven't read, will have a special icon nearby (little "eye" icon by default, forcing you to "see" that topic). If the topic has been "read", no icon will be present.

eye? how to do it?

but on the homepage do not see that this topic is a new post

You must be logged in to see that icon, this feature is for members only.