The first mobile phones were heavy and clumsy to use, but nowadays they are much easier to handle.
I think there should be the comma after the word "nowadays" like in:
"Nowadays, I bake my own bread rather than buy it."
Does we need the comma?
Punctuation is a matter of orthographic convention. The primary purpose of punctuation is to reflect the clausal structure of a sentence. The secondary purpose is to identify phrase boundaries where the absence of such markings could result in loss of clarity.
There is no grammatical requirement to separate clauses or phrases using punctuation marks, and a sentence does not become ungrammatical when no punctuation marks demarcate its clauses and phrases.
In the worst case a sentence if it is complex in its structure becomes unclear to the reader when it lacks punctuation.
In your example sentence you can use a comma or omit a comma after nowadays.