DD is 7mo and though she wriggles in it, she can't get out of it. I also only use it on the floor on top of the thick rug. Tbh, even if she did fall out of it, she's only falling the height she would if she fell over from sitting which even 'competent independent sitters' sometimes do.
How they can be classed as dangerous, when used correctly, is beyond me.
I also haven;t found it to hinder DD sitting as she has been able to sit unsupported for some time.
They make a great little chair for weaning in 