kono hasami ha yoku kireru node, kami wo kiruno ni benri desu.

この must be followed by a noun, while これ stands alone.

• この はさみ = these/this scissors
• これ = this one / this

So if you want to directly name the object as scissors, you use この はさみ.

Compare:

• これは よく 切れる。 = This cuts well.
• この はさみは よく 切れる。 = These scissors cut well.

Both are possible, but この はさみ is more specific because it names the item.

Japanese nouns usually do not show singular vs. plural the way English nouns do.

So はさみ can mean:

• a pair of scissors
• scissors

The number is understood from context. In English, scissors is grammatically plural, but in Japanese はさみ is just a normal noun with no special plural marking here.

That means この はさみ is naturally translated as these scissors or this pair of scissors, depending on the context.

Here, よく is an adverb modifying 切れる.

In this sentence, よく 切れる means something like:

• cuts well
• is able to cut well
• is sharp/effective at cutting

So よく does not mean often here. It means well.

This is a very common point because よく can mean different things depending on context:

• よく 行く = go often
• よく わかる = understand well
• よく 切れる = cut well

切る means to cut, while 切れる can mean can cut or cuts well / is sharp enough to cut.

In this sentence, 切れる describes the scissors as having good cutting ability. It gives the nuance that the scissors work well or are sharp.

So:

• この はさみは 切る。 would sound odd, because it would literally suggest these scissors cut in a more direct, less natural way.
• この はさみは よく 切れる。 is the natural way to say these scissors cut well.

This use of the potential form is common with tools:

• この ナイフは よく 切れる。 = This knife cuts well.
• この ペンは よく 書ける。 = This pen writes well.

ので means because or so, and it connects the reason to the result.

Structure:

• よく 切れる ので = because it cuts well
• 紙を 切るのに 便利です = it is convenient for cutting paper

So ので introduces the reason why the scissors are convenient.

Compared with から, ので often sounds a bit softer and more explanatory.

• 切れるから、便利です。 = also correct, a bit more direct
• 切れるので、便利です。 = a little more formal or gentle

The の turns the verb phrase 紙を切る into something noun-like.

• 紙を切る = to cut paper
• 紙を切るの = cutting paper / the act of cutting paper

This nominalized phrase can then be used with に and adjectives like 便利.

So:

• 紙を 切るのに 便利です = is convenient for cutting paper

You can think of V + の here as similar to English -ing in some cases.

Here, に marks the purpose or use.

The pattern is:

• Verb-dictionary form + の + に + 便利
• Noun + に + 便利

It means convenient for ... or useful for ...

So:

• 紙を 切るのに 便利です = It is convenient for cutting paper.

More examples:

• 料理するのに 便利です。 = It is convenient for cooking.
• 勉強に 便利です。 = It is useful for studying.

So に here is not a location marker. It is showing the purpose/use.

Because 紙 is the direct object of 切る.

• 紙を 切る = to cut paper

The particle を marks what the action is done to.

So in 紙を 切るのに, the full mini-phrase is still there:

• 紙 = paper
• を = object marker
• 切る = cut

Even though the whole phrase later becomes 紙を切るの, the object marker を stays because 紙 is still the thing being cut.

は marks この はさみ as the topic: the thing the sentence is about.

So the sentence is basically saying:

• As for these scissors, because they cut well, they are convenient for cutting paper.

Using は makes sense because the speaker is introducing or commenting on these scissors.

If you used が instead, the nuance would change. が would focus more on identifying or highlighting the scissors themselves, while は presents them as the topic under discussion.

For a general descriptive statement like this, は is very natural.

It is describing the scissors.

The structure is:

• この はさみ は ... 便利です
  = These scissors are convenient ...

And 紙を切るのに explains what they are convenient for.

So the meaning is not cutting paper is convenient. The meaning is:

• These scissors are convenient for cutting paper.

That is an important distinction. 便利 is attached to the main topic, この はさみ.

Sometimes learners wonder about this because both can relate to purpose, but here のに 便利 is the natural pattern.

• 紙を切るのに便利です = natural, common
• 紙を切るために便利です = unnatural here

Why? Because 便利 often pairs naturally with 〜のに to mean convenient for doing ...

So when talking about usefulness or convenience, 〜のに 便利 is a standard expression.

Examples:

• この道具は 野菜を切るのに 便利です。
• このアプリは 日本語を勉強するのに 便利です。

So for this sentence, のに is the right choice.