The 8" wodent wheel has small round holes
I think the Silent Runner is great for a dwarf hamster but I was a bit concerned about it for a robo as robos are so small - so my personal choice was between an open wheel and an 8" wodent wheel (called the Robo wheel in Germany). It could be fine of course - I was being ultra cautious.
9" Silent Runner
Silent Runner 9 Inch
8" Junior wodent wheel
https://www.rodipet.de/shop/laufraed...isspurpur.html