roundings

Has anyone come across any roundings where the top 'rein' is elastic and the bottom is leather? So when it is pulled, to start with the snaffle part is in action, and if it is pulled more the elastic goes to full stretch and becomes the same length as the leather 'rein' therefor putting action...

What are your opinions on Pelham bits as I am thinking of trying it out. What are your experiences, is it worthwhile to get roundings or the double rein?