Ten segregator jest praktyczniejszy niż tamten.

Because ten has to agree with segregator in gender, number, and case.

• segregator is masculine singular
• here it is in the nominative case, because it is the subject of the sentence
• the nominative masculine singular form of this is ten

So ten segregator means this binder/file.

If the noun were different, the form would change, for example:

• ta teczka — this folder
• to pudełko — this box
• te segregatory — these binders

Tamten means that one or that.

It is the opposite of ten:

• ten = this
• tamten = that

In your sentence, tamten stands for tamten segregator. Polish often leaves the noun out if it is obvious from context, just like English can say this binder is more practical than that one.

It is in the nominative case.

That is because segregator is the subject of the sentence:

• Ten segregator = the thing being talked about
• jest praktyczniejszy = is more practical

So the basic pattern is:

• subject in nominative
  • jest
    • adjective/comparative

It is the comparative form of praktyczny.

• praktyczny = practical
• praktyczniejszy = more practical

Polish often forms comparatives by adding endings such as -szy or -ejszy / -niejszy, sometimes with a small stem change.

So instead of using a separate word like English more, Polish very often builds the comparison directly into the adjective.

Other examples:

• tani → tańszy — cheap → cheaper
• ładny → ładniejszy — pretty → prettier
• wygodny → wygodniejszy — comfortable → more comfortable

Yes. Ten segregator jest bardziej praktyczny niż tamten is also correct.

Both mean more practical, but there is a difference in style:

• praktyczniejszy is the single-word comparative
• bardziej praktyczny is the periphrastic comparative, built with bardziej = more

In many cases, Polish prefers the single-word comparative when it sounds natural, and praktyczniejszy sounds perfectly normal. But bardziej praktyczny is also acceptable and understandable.

Niż means than in comparisons.

So:

• praktyczniejszy niż tamten = more practical than that one

It is the standard word used after a comparative adjective.

There is also another common comparison pattern with od:

• Ten segregator jest praktyczniejszy od tamtego

That also means This binder is more practical than that one.

So both are possible:

• ... niż tamten
• ... od tamtego

Because niż and od behave differently.

With niż, Polish often keeps the same case as the compared item, or treats the second part like an omitted full phrase:

• Ten segregator jest praktyczniejszy niż tamten [segregator]

Here tamten is standing in for tamten segregator, so nominative makes sense.

With od, the word after it must be in the genitive:

• od tamtego

So:

• niż tamten — correct
• od tamtego — correct

This is a very common thing learners notice, so it is worth memorizing as a pattern.

In normal standard Polish, jest should stay here.

• Ten segregator jest praktyczniejszy niż tamten — standard and natural

If you remove jest:

• Ten segregator praktyczniejszy niż tamten

it sounds incomplete, very colloquial, or like a note/headline rather than a full standard sentence.

So for learners, the safest rule is:

• with this kind of sentence in the present tense, keep jest

Yes, but the original order is the most neutral and natural:

• Ten segregator jest praktyczniejszy niż tamten.

Polish word order is more flexible than English, so you can move things for emphasis. For example:

• Praktyczniejszy jest ten segregator niż tamten.
  This puts extra focus on more practical.

• Tamten segregator jest mniej praktyczny niż ten.
  Same idea, but now the sentence is built from the other object.

Even though other orders are possible, the original sentence is the best default pattern for a learner.

Because it agrees with segregator, which is masculine singular.

In the dictionary, many Polish adjectives are given in the masculine singular form, and that is what you see here:

• praktyczny — practical
• praktyczniejszy — more practical

If the noun changed, the adjective would change too:

• Ta teczka jest praktyczniejsza — This folder is more practical
• To rozwiązanie jest praktyczniejsze — This solution is more practical

So the ending is not random; it matches the noun.

Yes. In Polish, grammatical gender does not depend on whether something is alive.

Segregator is masculine inanimate. That is why it takes:

• ten segregator
• praktyczniejszy

Many object nouns are masculine, feminine, or neuter just because of their grammatical class, not because of any real-world sex or animacy.

So when learning a noun, it is helpful to learn its gender together with it.