Are MCBs and consumer units of different makes compatible with each
other ?

I have a Clipsal consumer unit and the Wylex MCBs in B&Q say they can
only be used in their NH range of Wylex boxes. However, on inspection,
they look the right size and are type B as per my existing ones. They
are also the same size.

I will be using the MCB on the RCD side of the consumer unit so does
the make of RCD device need to be specific to the MCB ?

Can anyone clarify ? Thanks.