If you want to go with the baby bjorn, I found a website comparing both baby bjorns with IKEA's potty- it was a while ago and don't have the link anymore. And being that Ikeas's Potty was $5!!!!! I made the trip there and now am a proud of owner of two $5 potties... that my DS refuses to train in anyhow!
FWIW, he does like to sit on it (although, I sewed a nice cushion bec. it is just a plastic seat and his tush gets red after sitting for a while), I think he is just not ready yet.
We are going to take a coupla week break from this training and hopefully he'll be ready to start fresh then.