How do I know this lid fits my Crock-Pot?

Check the part number on your cooker or its old lid. This assembly is 173660000000 and is made for Crock-Pot casserole models that use that number. Lids from other models and sizes will not fit.

Is this a complete lid or just the glass?

It is listed as a lid assembly, so it is the lid as a unit rather than a bare piece of glass. Confirm against your model's parts list before ordering.

Can I use it on a different brand of slow cooker?

No. It is a Crock-Pot part made for specific Crock-Pot casserole models. Another brand's pot will have a different rim and diameter.

Is it worth replacing the lid instead of the whole cooker?

If the cooker itself works and only the lid is damaged, a genuine replacement lid keeps a working appliance in use. A new cooker only makes sense if the pot or heating base is also failing.

Does it come with a handle?

It is sold as a lid assembly under the Crock-Pot part number, which covers the lid as supplied for that model. Check the parts listing for your cooker if you need the handle separately.