How popular will this be?

There has been plenty of controversy over this product.

They say:

Rainpal says fits most existing helmet visors (Full, Flip or Open). 

Rainpal’s wipers are detachable for replacement.

Like any electromechanical device there is always a trade off between battery life and functionality.

Rainpal’s optional wiper will have an adjustable tension shaft so that urban riders get longer battery life by reducing the pressure of the wiper on the visor and if riding faster on open roads one turn with the rider’s finger of the adjustment control knob near the top of the shaft will increase the wiper pressure on the visor and keep the wiper wiping clearly and not skipping at higher speeds.