I have Doyle's blackberry, just one plant and I think I remember it was kind of slow to start first year. Not 100% sure, it was 5-6 years ago. Want to say that it was worth waiting. This blackberry production is outstanding. I have it side by side with Triple Crown and it produces probably 4-5 times more berries, even though TC is quite productive too. Really amazing.
Olga

We had 20 planted and as long as you live in a place where it cools down at night or if not they're planted in an area with afternoon shade, they'll do great. We live down near Montgomery AL and they started to ripen in late June when it's 90+ during the day and a humid 70+ degrees at night. We would get a couple of pickings and then they would burn up in the heat.

However, as Olga mentioned, they are slow to start, but once they do, they are quite hardy growers.