Running a log splitter in vertical mode is physically demanding work. Log splitters don’t split them in two all the time and you have to pull them back, spin the chunk and start splitting from another angle.
I have split tons of oak and they can be stringy where they don’t split clean for a splitter.
My cousin (45 years old) and I (21 at the time) had a race. I had only ever used a log splitter (35 ton) and he only ever a maul. We both cut 10+ cords a year.
He helped me split up a oak tree I dropped that could potentially fall on my mothers house with the right wind so I dropped it.
We both cut the tree into 15-18in pieces, I took the knotty wood and him the strait grain sections. After 2 hours out piles were about even and I was hustling, driving the ram as fast as the splitter would go slinging chunks of wood.
The next week I bought a maul and found out, in many cases for me the maul was easier and faster to use than running the splitter. Mainly because I could reset and swing a maul faster than spin a chunk and wait on a slow cylinder to drive a wedge. And I could bring the maul to the wood vs having to roll the wood to the splitter. I would only bring the splitter in for the knotty wood.
Two types of maul I would buy, the axe with the mechanism in the head to split the wood or those nice fiberglass handle maul with the splitting head they sell at TSC and rural king. They are light enough to swing at a good rate, I have used those heavy ones and after 10 swings I’m ready for a break lol.
I’m 29 now, I would go at it with a sharp maul first, then rent a splitter for what’s left.
20 tons will prob be fine, my cousin later bought a 20 ton splitter. I like the huskee 35 ton but lighter should be fine.