Acrylic glass, sometimes known as the brand Plexiglas® and Polycarbonate, sometimes known as the brand as Lexan®, are sometimes considered as a replacement for tempered glass, especially in exterior applications. They are more of a plastic than glass and tabletops made of them have very distinct advantages as well as disadvantages. Acrylic glass is lighter and is easier to carry. For that reason, and their ability to be readily packed, they are cheaper to pack and ship. They also may hold up a little better in extreme conditions like a picnic area under white pines that shed their branches. They are not indestructible but may survive better than "normal" glass.
There are significant disadvantages as well. Acrylic glass can scratch very easily and even paper towels are not recommended to be used on them. Ammonia-based cleaners will attack them. One of the benefits of acrylic is its flexibility. However, in an open top application, they may not hold weight very well and can bow. Also, while great strides have been made in preventing acrylics from yellowing, they still tend to weather over time. Lastly and arguably, the most important disadvantage is that acrylic does not carry the beauty of glass.