There are four round looms, sure, and they have different numbers of pegs, sure, but they also have different gauges!
I measured the distance between the pegs for each loom, and it was as follows:
24-peg loom: 8mm
31-peg loom: 10mm
36-peg loom: 12mm
41-peg loom: 13mm
At least the pegs themselves are all the same size (7mm in diameter).
Is this normal? I mean, I obviously bought a cheap imitation of the "real thing", but do real official knifty-knitter round looms also display this difference in gauge between looms? Because all my straight looms have the same gauge (5mm pegs, with 12.5mm between each peg), unlike these ones, so I assumed that was standard. However, if having different gauges as well as number of pegs for round looms is standard, then I'll just have to live with it.