Tā wéirén hānhòu, dàjiā dōu yuànyì gēn tā dǎ jiāodao.
He is a guileless, decent sort, and everyone is happy to deal with him.
Tips
usage
A compliment about character, not a comment on intelligence. It praises someone unguarded and decent. On its own 憨 does lean toward dopey, so it is the pairing with 厚 (generous in nature) that makes the word warm.
culture
The same 憨 turns up in 憨态可掬, the stock phrase for something endearingly clumsy, the line Chinese media reaches for whenever a panda is on screen.