Here's my experience - but warning - it's uncommon and most people here would be opposed to what my budgie and parrotlet do.
Ok - so, I got Pi first. He's a Petsmart budgie. I had two, but Lemondrop died suddenly (way too young) and I knew I didn't want to get another Petsmart budgie. I found Kalypso (my parrotlet) through a local breeder. She was just weaned when I got her. I would make her sleep in a separate cage, but during the day I allowed them to play in the same, very large flight cage. After a few months, I just let them stay together. Pi is EXTREMELY skittish. I have had him for three years now (I saw that questioningly as my memory is terrible) and he is just starting to be more comfortable with my hands. I don't push it. Kalypso loves me, but she ADORES Pi. She will protect him at all cost. I have never had them harm each other and I think if I tried to put them in separate cages, they would be heartbroken. They are completely bonded. This is NOT the norm. I honestly am not sure I it happened - Kalypso was very young and Pi very scared. She "protects" him from me LOL - literally, in the morning will will fly at the door when I wake them up to make sure it's ok. They are always beside each other and always preening each other.
Now, I had some people tell me to separate them asap. I tried, it was bad, I refuse to do it again. That was part of why I stopped coming to the forum for a while as I was made to feel quite horrible for having them together. But it works for THEM and that's what matters.
Whether you get one or not is completely up to you and your heart. Would yours be able to live with your budgie - doubtful, but given the right set of circumstances, they can definitely interact - so long as both end up happy, healthy, and loved. Parrotlets are very much like feisty little dogs! If you know how to train and love them, they are worth it.