"I heard such pens write well." is correct. Note that my initial preference was to write, "I've heard such pens write well." because "I heard" sounds colloquial to me, although I do think it's correct as well. 'Good' is an adjective used to describe nouns. 'Well' is an adverb used to describe verbs. Since 'write' is a verb, you need the adverb.

I heard writing of such pens good.