Every glass block breaks instantly in the Glass Cutter's hands - no more chipping away at panes one tick at a time. What you get back is entirely up to which mouse button you swing with.
Both behaviors are baked into the tool itself and always apply - there's no toggle to remember and no enchantment to manage.
The dual left/right behavior above is the tool's Silk Touch - so the enchantment itself is explicitly blocked from being applied to it (it just wouldn't make sense to stack a permanent Silk Touch on a tool whose right-click function depends on not having Silk Touch). Every other applicable enchantment - Efficiency, Unbreaking, Mending, and so on - works completely normally.
Any glass-family block: plain and stained Glass, Glass Panes and stained Panes, Tinted Glass, Glowstone, and Sea Lanterns - all break at full instant speed regardless of tier, though higher tiers still carry more durability and a better enchantment ceiling.