That is about it.

Both work, to my ear.

You're collecting, or assembling a group of things. You may be doing it physically or intellectually.
When you've finished, you may keep them in your possession, or you may "hand them over" to someone else.
If you wish to call attention to their being in your posession, you could say, "This is about it."
However, "that" is more common.

The expr

ESLBeginnerI'm wondering why it is "That" is about it, not "This" is about it?

that refers to what precedes. this refers to what follows. So you can start your discussion with This is about it, then say your piece, or you can say your piece and then say That's about it.

Likewise, we say This

I'm inclined to give the speaker a bit of lattitude. I think he may choose the pronoun which conveys his desired meaning.

A man comes to your house and requests that you give him his wife's clothes.
You scavange about the house and present him with the collection.
"This is about it." "This" refers to the pile of clothes in your arms.
"That is a

AvangiI think he may choose the pronoun which conveys his desired meaning.

Let's hope he does!

Avangi"This is about it." "This" refers to the pile of clothes in your arms.

But this example doesn't apply to time (or its equivalent in a text). It's a normal use of a demonstrative pronoun to refer to what

Hi, Jim,
Your first post caught me off guard. I sensed you were placing it in a temporal frame, but I had no idea why. It seemed like a general statement about the choice of pronouns.

Perhaps my problem is that "A million words. That's about it." carries some meaning I'm unaware of. I'm lost.

AvangiPerhaps my problem is that "A million words. That's about it." carries some meaning I'm unaware of. I'm lost.

Let's see if I can find you.

Okay. Got it. Thanks.