The plastic ones do have their disadvantages in being 'springy' as has already been mentioned. However, they are easy to clean - just give them a good scrub in hot water with lots of soap, and any wax and propolis will melt straight off.My conclusions are that plastic will be difficult to keep clean and free of brace comb, and could be easily damaged beyond repair by vigorous application of the hive tool. You can't blowlamp them either to burn off propolized deposits. Whereas the flat steel ones are relatively heat proof.
We all seem to be forgetting the importance of BEE SPACE. Any framed excluder will increase distance above and below frames encouraging use of propolis and brace comb, no wonder removing excluder is a problem. Have used may types of Q excluder and come back to the slotted zinc type. It can be 'peeled ' off yet regains it's shape when replaced. Tried plastic but always covered in brace comb ( again it increases 'bee space ') Haven't used wire ones since seeing problems and upset to Bees while removing it. Same with crown boards. Framed on both sides, Too much space, brace comb! Feel that manufacturers are taking profit rather than good of bees into account, and 'shooting us a line'.Hi Marvin
There are similar issues with other designs too. When you start to feel resistance to lifting, just slide it to and fro sideways a little to release it from the grip of the wax below.