Use them for green onions. Sets are long day onions that don't start bulbing until late June. They are notorious for bolting because they are last years growth. Yours is most likely Red Wetherfield. When you want bulb onions use plants appropriate to your area.

I had sets in the ground from last year that did the same thing. I pulled them and used as green onions. I do however have one still in the ground beginning to bulb. It does have a flower but it is not huge yet like the others got.
I planted sets this spring as well and so far so good no bolting. I hope they bulb up in July.