The Rodipet food seems good. I mix it half and half with Harry Hamster for my Syrian. The difference between the Junior and Senior is mainly the ratio of Protein to Fibre. Over 18 months old it is recommended that hamsters have around 15% protein, and higher Fiber (~12%). This is meant to help prevent Kidney issues, and keep digestion flowing. I found this info here
https://www.hamstersociety.sg/hamste...ty-and-quality it may be that different countries recommend different amounts, so do look around and decide for yourself.
Compared to Harry Hamster the Rodipet food is very expensive, so I understand that not everyone will be able to go for this option. If the pieces of Harry Hamster are too big for little Robos I don't know whether breaking them up a bit with a pestle and mortar might help? Again, I'm not an expert, and I haven't had Robos, so do read around and take in the opinions of others too.