The OP posted up those photos and asked for opinions, and I’ll expand on mine. Ultimately, this issue is between him and spike.
I’m not a welder, I won’t begin to speak towards the quality or structural integrity of that weld. What I do see is a deep crevasse in the side wall of that fermenter. Going forward using it that way, I would equate it to fermenting in a plastic bucket after someone has taken a hot knife and made a deep gouge in the side of it. No home brewer I know would continue using that bucket.
I understand the explanation of the full pen weld. Some distortion or waviness on the inside, fine. A raised bump or otherwise visible weld bead, fine. What I’m seeing in those pictures, not fine. Personally, I would return that unit. Regardless of whatever reassurances I receive from spike, I wouldn’t settle for that after dropping that $$ on it.