How bad is it to freeze vegetables in glass for a maximum of 4 weeks?
The main effect that reduces the quality of food that is stored in the freezer is freezer burn. This is basically dehydration, caused by the very dry air in the freezer. Any container that seals airtight prevents this from happening, so your vegetables should stay good.

With glass containers, you may have to be careful to prevent them from cracking. If there is a lot of liquid in the food you want to freeze, you have to take care to leave enough empty space in the container to allow the water to expand as it freezes. With containers that have a very rigid lid (like jars with a metal lid) it can be a good idea to freeze with the lid placed only loosely on top, and then tighten the lid as soon as everything is frozen, to avoid having a lot of pressure inside the jar from the expanded water.