1. On the one hand, he is very kind. On the other hand, he is very poor.

2. On the one hand he is very kind, but on the other hand he is very poor.

3. On the one hand, he is very kind, but on the other hand, he is very poor.

4. On the one hand, he is very kind. However, on the other hand, he is very poor.
------------------------------------
Are they grammatical? Would you check the commas? Do you have better expressions?

#s 1, 3, and 4 are best. 2 is missing some needed commas.

All of the given sentences are grammatically correct but have slight differences in punctuation. Let's analyze each sentence and discuss the usage of commas.

1. "On the one hand, he is very kind. On the other hand, he is very poor."
In this sentence, commas are used correctly to offset the phrases "on the one hand" and "on the other hand." The comma after each phrase helps separate them from the main clause. This sentence is grammatically well-structured.

2. "On the one hand, he is very kind, but on the other hand, he is very poor."
This sentence is also grammatically correct. However, unlike the previous sentence, it uses commas both before and after the coordinating conjunction "but." While it is not necessary to have a comma before "but" in this case, it is still acceptable and does not cause any grammatical errors.

3. "On the one hand, he is very kind, but on the other hand, he is very poor."
This sentence is the same as sentence 2 and is also grammatically correct. The use of commas around "but" is optional and does not affect the grammatical integrity.

4. "On the one hand, he is very kind. However, on the other hand, he is very poor."
This sentence is also grammatically correct. Instead of using the conjunction "but," it uses the conjunctive adverb "however" to join the contrasting clauses. The comma after "however" sets off the conjunctive adverb and is necessary for correct punctuation.

Regarding better expressions, the sentences provided are straightforward and clear. However, if you wish to make them more concise, you can consider using phrases like "while" or "although" to convey the contrast:

- "While he is very kind, he is very poor."
- "Although he is very kind, he is very poor."

Remember, the choice of expressions depends on the context and the desired impact of the sentence.