I use these for supers.
Several issues though.
1. Using MDF for bars - the tiny 'tabs' that need to be created in the ends of the wooden battens - which snap into the plastic to hold plastic to wood, can easily tear off and so pop the wood from the fitting. Same happens with ply. Solution - need to use glue to hold bars into plastic fitting. Makes re-use difficult.
2. I found that the side bar often pulled away from the bottom bar, in the honey extractor. Always the bottom one so maybe the frame holder in the extractor is at fault. Solution - need to use glue to hold bars into plastic fittings.
3. For 14x12 frames, MDF bends too much under the weight when filled. Solution - don't use for these. I only use them for supers now.
Advantages are that frames are v easy to build, although creating the wooden battens is tedious. Also, bees don't propolise the plastic frames to the wooden supers. So easy to remove.