You might be surprised, though.
I have a LG still air incubator from
TSC - I actually have two - and have had what I think are successful hatches for a few years now. The first batch this year yielded 18/28 chicks (some of the eggs just weren't fertile and 4 eggs just didn't hatch), then I got 10/15 ducklings out of the same batch and now I'm waiting for my second and third batches of chicks and ducklings - 46 chicks are due 4/27 and 16 ducklings on 5/13. So far 95% of chick eggs are viable - duck eggs are too soon to candle.
With the first batch of chicks and ducklings I put both types in together on the same date. During the first week I made a huge mistake and messed with the temp (that had been reading 99.5 for a day as I warmed it up) about 3 hours after I put the eggs in - so I spent the next few days getting it to regulate again.
About 2 1/2 wks in we also had a temp spike so I spent about 2 days fixing that. I was nervous, too, that I had lost most, if not all, due to the inconsistancies in temp, but ended up with a total of 28/43 eggs - 65%. I know it's not perfect, but it's better than my hens are doing. Of course, if you're striving for 100% then, yes, you should invest in a better incubator. Last year I only did two batches and got 68% the first batch and 77% the second; the year prior I was starting out and got 80% on the first and only batch. But when you're just trying to make the animals pay for their own feed that isn't bad.
Both my bators have been running with the second and third batches now for a week and I've had no issues with temp. If you think about it, hens don't sit on their eggs 24/7 - I've had several hens get up off their nest the entire day, leaving me to wonder if I should take the eggs and throw them out, but I left them in and a few weeks later several peeps could be heard from the hen house...
Good luck - I'm sure you'll end up with a few good ones!