The sentence "It functions well" is correct and can be used in written English.
For example, you could use it in a report, such as: "Our new system has been tested and it functions well."
AllMusic's Heather Phares described the album as more consistent than most remix collections and noted that it functions well as a record in its own right.
If a kitchen is well designed, it functions well.
Taege said it functions well as it is.
He said that the park "didn't function for what it was designed for" — an under-the-bridge plaza for people to sit — "but it functions well now".
"The beautiful thing about tiki," he said, "is that it functions well in tropical climates, like in Florida and California, but it works just as well in the snow or in a harsh urban climate like New York.
It does seem like a rather logical use for a maps mashup, and it functions well.
When the proposed bowl-rotatable blade system was testes by dry run it functioned well but, when the bowl is filled with water and melon dices it functioned badly.
It functioned well as nunnery during her time and also during the next generation but went into decline thereafter.
Notwithstanding the field's many success stories, it still functions well under the radar of the mainstream media and national consciousness.
Furthermore, when it is busy detoxifying alcohol, it cannot perform its functions well either.
