Parrotlets are feisty and stubborn, often described as having Napoleon complexes due to their small size. They can be friendly, but it is entirely based upon the level of socialization you give them. Handle them often and they will be more used to you, and less likely to bite when approached.
They are very small and fragile birds. Due to their size, it is easy for them to be stepped on, sat on, rolled over on, or otherwise harmed unintentionally by our giant, clumsy limbs.
They are not very loud, which makes them a great bird companion to have. They are very interactive, unlike other small birds (budgies, finches, etc) and will gladly share in your company by playing with toys or chirping quietly. They can be cuddly.