I bought a trial pack of these. My impression - do not bother. They will give you nice - nearly perfect spirals. But you have to rip your hair through the curler and you cannot sleep in them in any reasonably human fashion. There is a lot of tension on the roots with these. Maybe for a wedding or something special paired with a bonnet dryer? Otherwise you're better off perfecting rag curls or working with your natural texture.
I absolutely loved Curlformers while I was transitioning from relaxed to curly hair. It was a great way of camouflaging my relaxed texture where it met my curly texture. Since I've completely transitioned to curly hair, and cut off all the relaxed texture, I have not used them. I think these work best on hair that is looser, straight, or in a relaxed state. As the previous poster stated, there is more tension at the roots, and this can be good for those who are trying to transition with tighter curls, because it helps them have the straight roots while transitioning and not puffy roots. The only problem that I see is that once you take the curlformers out you can only maintain the spirals for so many days. I would definitely recommend this product for special occasions also.