Sure, I've used them. They're fine. There are some cross-compatibility issues that crop up every once in a while, but you're going to find that with any non-MS Office application suite. Apple definitely also pushes using its native format over exporting, but you can do it. If you don't care that your docs all end in .pages or .numbers or .keynote, then there's no reason not to use them.
If you have a Mac newer than, say, 2013, they should have come free with your computer.