Recommendation for a good, long recording app on android

First, I'm not an android user, I'm an IOS user. I have need of hiring a short-term reader for a project. I've found one but she uses Android. What app would you all recommend she use for recording? Requirements:

1. free
2. can record for hours at a time, no recording time limit.
3. easy to use.
4. can export .mp3 or .m4a files Thanks!