Seramas can be tough to hatch regardless of incubator. And I've seen a lot of broodies ruin hatches as well. It's why I started incubating - because I was too often left with the results of pea brained brooding.
I have only done two serama hatches, one was just two eggs. Then I set 25, only 10 made it to day 18 and six of those hatched and one died later. The other five were worth the trouble.
It's not the incubator - it's the eggs and the art. And if you do it often enough I am told you get better even at these tiny eggs. I hatch in an incubator a LOT of my own and shipped eggs that aren't serama and get great hatches in both my homemades and my antique redwood cabinet bator.
I'm still fiddling with the right humidity and other things that might just play a role when hatching seramas but part of it's genetic, there are lethal genes in Seramas and I think small eggs loose rather more moisture than most over a hatch so I'm fiddling with that.
I got my last five just running them the same as my own eggs. Most were clear so I know it wasn't just the incubation, then a few middle run quitters and then 10 at the end.
I think there's a learning curve with them rather than any ONE incubator. There is rarely any Magic to incubation. And nature aka Broodies also fail though in some cases a well seasoned, well practiced broody can excel at difficult eggs. Or not, they do have brains the size of peas.
I prefer, since mine free range and are not separated from the flock, to incubate precious eggs myself now.
And this time of year brooding outdoors has a lot of hazards. We had a freak storm and freeze yesterday and a broody with three chicks lost two of them to the damp and cold before she could round them up and get them warm. Fortunately they were just mixed chicks to keep her happy anyway.