You can slouch just as well on an expensive throne as you can a cheap one. In my opinion posture isn’t a throne issue, it’s an awareness and correction issue. But I digress..
This is very true, which is why I use a Tama Ergorider with backrest. I don't really lean against the backrest, but it gives me a proprioceptive cue to maintain posture and to sit on my butt, not my spine.