Hydraulic splitters! Pfft.
I cut a lot of wood each year and don't rate hydraulic splitters either. But I don't have much knotted timber.
I reckon they're harder work than swinging a log splitter. First you have to have all your timber arranged so you can roll the hydraulic splitter down the line so you're not tripping over while carry timber to the machine, but you still have to lift each piece waist height onto the machine, which kills my back pretty quick.
Splitting logs is not that hard, and very therapeutic for a non-violent person like myself. First dial your aim in so you're not wasting blows, and then work out if the log needs to be split radially or grid pattern. I usually don't have a single block to split on, but move around using new blocks to minimize carrying, sometimes splitting stuff where it sits.
I got into a bit of race one year with the father in law and mate who where using there new 30t splitter, and by the end of the day they hadn't cut that much more than me, certainly nowhere near twice as much, and they were just as tired as me.