Composite ratchets are made from nylon or similar plastics, and they're honestly fine for most casual riders. They're lightweight, functional, and you'll find them on plenty of entry-level and weight-conscious bindings. If you're hitting the resort a handful of times a season, they'll serve you well without issue.
The trade-off is long-term durability. If you ride hard and often, composite ratchets can wear down or strip faster than aluminum or magnesium options. They're also a bit more prone to icing up in wet, slushy conditions, which can make them harder to crank tight on cold mornings.
Don't write them off, though. For weekend riders and those just starting out, composite ratchets work great and keep your setup light. If you're logging 50+ days a season or find yourself cranking straps super tight, that's when aluminum becomes a worthwhile upgrade.