Today I bought a ready meal (chicken with potato wedges) which stated, in bold letters, "not suitable for microwave cooking" in the instructions.

Being the rascal that I am, I microwaved it, and it was perfectly good. Why do manufacturers say this on some products? I just wondered.

It will probably be the potato wedges. Not from a safety aspect but quality. They would reheat better in the Oven than the microwave.

Quality of the "finish".

Things that are supposed to be crispy, or browned for example, won't come out like this if heated in a conventional microwave.

You can cook most things in the microwave without health fears, but many (like potato wedges) will suffer in terms of texture and quality.