I have this exact stool (the Cars one), and a similar foldable seat.
The foldable seat is a lifesaver when you're out and about. It fits easily into a diaper bag, and it can be placed on those gigantic toilets in many public restrooms. The seat locks open easily - I've never been even mildly concerned about pinches or splashdowns.
But when I don't have it, then I AM worried about my kid falling in when the only option is a handicapped seat. Ever tried to hold a three-year-old on a handicapped public seat while keeping the one-year-old from chewing on the feminine products receptacle? Well, it's not pretty. But the folding seat - saves the day.
The stepstool functions as advertised. No problems or glowing review there. The other seat is ok. I don't have this model, but a neighbor does, so I've seen it in toddler action. The splashguard isn't great, but at least it's removable.