The problem, as I see it, is that microwave radiation (typical 2.45 GHz) is absorbed very well by solvents and/or reacting chemicals, and this phenomena does not allow sufficiently deep penetration of the radiation into the bulk of reaction mixture. Various designs were proposed to deal with this issue, but it is still difficult to overcome the mentioned fundamental challenge and make microwave reactors applicable to a large scale.
Yes! It is similar to photochemistry in this respect.
However, as in photochemistry, flow reactors is the way to go, I wish to thank Dr. Mushtaq Ahmad for providing two very good references, which also include what I just said about the advantages of flow reactors.
Microwaves method is used on large scale but not much . This is because the formation of the isomeric products . Power control and size of the reactor are some problems. Thanks Dr. Mushtaq Ahmad for citing references.