OP, are you in a non-freezing location? Any of the ground drive machines won’t work dispensing frozen manure if you leave it sit overnight. Warm manure will freeze together into a big lump stuck to the machine. Ground drive usually is not up to breaking the lump loose. Chains will break, wheels won’t turn on Newer types.
My son left a load sit overnight, took him several hours to break the frozen manure load apart in the Millcreek spreader to get it out with a fork and shovel. Temps had been below zero and we did not know he had not dumped the load!! Frozen manure stuck to walls, floor, chains is hard to get out! He NEVER did that again. This can happen in both the Millcreek and Newer spreaders.
If you load them, then spread right away the unloading works fine. Not sure how the Newer spreader would do spreading frozen poop balls, with the smaller slotted opening on the bottom. You could just tip it backwards to dump the load out, not spread it when poop freezes in stalls. It had no problem with fresh, unfrozen manure, but not everyone can get stalls cleaned right after horses go out. Millcreek had no problems with frozen poop balls when spreading them.
I found the Newer spreader to run small in poop volume when cleaning our stalls. It was supposed to hold 8 stalls worth I think. I could only get 3-4 stalls worth in and they were TIE stalls that use half the bedding of a box stall. Tie stalls are cleaned to the floor daily, there is always a quantity of wet sawdust bedding in them, along with poops. So it was a surprise at how little it held. I ALWAYS had to make two trips or more, to get our 8-9 stalls cleaned. I sold it on. I loved the Millcreek but it got hit by a speeding truck, looked like a pretzel! Son was uninjured by a miracle, tractor stayed upright, though it hopped into the shallow ditch.
We found a nice, elderly, PTO driven spreader after the Millcreek was killed. We are on the third one after wearing out 2 over the years. Could no longer be repaired. I love the PTO which lets me spread or dump the load in a pile if ground is too muddy for spreading. Husband keeps it going by replacing the floor boards, chains and spreader bars as needed. Prices for this size older spreader have gone up incredibly over the last few years!