I made a guitar amp head cab years ago, tolex & items from Marshall, but never got round to fitting protective corners. I bought these and the whole cab looks in a different league. It looks real pro' and has good knock protection.
You have to be careful with corners though for their internal radius, sometimes a homemade cab will have square corners and these will not sit properly, in fact most corners plastic or metal have an internal radius, so if you are making a cab make sure that you round off all edges and corners if you want to fit case corners.
These metal ones are good quality and not only protect your tolex covered cab but also protect the roof lining of your car if you dont have a Transit gig van!