I have never had good luck with uniseals, they always seem to leak. Even if it's not right away, they all eventually end up leaking.
Schedule 80 bulkheads have a thick enough gasket to "smoosh" into not flat surfaces.
At my previous house I had two installed in barrels that never leaked a drop in 8 years. They usually do fine for me and I've probably used a couple dozen of them over the decades. I was really surprised it leaked!