The thing with babies is that you never know what they will take to. That's why for these things my tip is not to buy super expensive products. If the design works for you, you can always get the expensive one later.
We first got a seat that goes on the actual pot. Didn't work on my son. Then we bought a baby potty that looks like the Combi one above, but from a regular local mom-and-pop shop so much cheaper. Turned out to be a toy, and it is now sitting in storage, never used.
Turns out my son likes the original seat that goes on the pot + footstool + noone must be in the loo with him. We have now guarantee that his baby sister will go for the same.