I shot them (340 spine also), eventually made my way through most of a dozen. Have a few left. No problems at all, they shot fine. A robinhood or two, can't remember what happened to the rest.
They take a smaller nock than my other Eastons and my center serving is no longer set up for them. About the vanes, without going downstairs to look, I thought they were fletched with Blazers which are a fine vane. As with any shaft, flex after each shot.
Being an inexpensive shaft, they'll likely have a stiff side so nock turning might help your groups. Of course being prefletched, that'll mess up the index vane color but a Sharpie mark could take care of that.