Smart glasses are being touted as the way of the future, but at least one person who’s worked on such projects isn’t quite so sure.

Snap’s latest generation of augmented reality Spectacles have been lambasted by one of the engineers who helped to create them. The glasses, revealed earlier this week, were described as “a disaster” by Sterling Crispin, a former design engineer for Snap.

Augmented reality glasses overlay digital images onto a person’s view of the physical world. They’re different from virtual reality headsets that fully immerse people into a computer-generated environment.