Um just a thought - how do they transport the ibc's in the first place when they are full of whatever fluid they carry? I suppose they are pretty stable when full.
IBC's are only ever transported full, and are generally single use tanks for the chemicals industry. When full, they are relatively stable,... but half empty the water sloshes around and can cause quite a bit of instability, especially on corners.
Self baffling can stop this sloshing and make the vehicle safer to drive,... but as far as I know, if you were involved in a crash with a self baffled IBC in the back of your van,.. no matter how well secured and baffled,.. your insurance would not cover you, and you could end up being prosecuted.
I've always been told that its not legal to have a tank larger than 250 litres in a van without factory installed baffles, even if its 3/4 empty!