I like it too. It reseeds a little in my yard, which I let it do, but it's not at all invasive for me. Seedlings are easy to pull if you don't want them.

A 'weed' is a bit different from a true invasive. Red valerian or Jupiter's beard, Centranthus rubra, is one of those plants that qualifies as a garden thug. Sold as an ornamental, it can self-seed to the point where it becomes a weed or spreads prolifically throughout the garden and sometimes into the neighbors. FWIW, this is often the way many plants which are now listed as invasive species started out......popular ornamentals with very freely seeding and weedy tendencies and an adaptability to a wide range of growing conditions.

If you have concerns, deadhead before the plants sets seed.

I love my Red Valerian. Hardy, healthy, blooms most of the summer, not fussy about watering except needs good drainage, attracts butterflies. The only care it needs is deadhead to promote bloom, and clean up the flower stalks once they've died.

Here is a link that might be useful: photo and basic info

It's never been invasive for me. I always dead head it to promote more blooms. I have never even had 1 seedling in my yard. I would just dead head it to avoid it spreading.