ck40n和ck11n一样，都是成本估算，只不过一个单个，一个是批量，目的是跑出该月的 standard price.
CK11N is for Single Material and
CK40N is for Multiple Materials. It could be to run all the materials in a plant or Co.Code or only part of them etc.
CK11N requires one more Activity (CK24) to update the price where as in CK40N, every thing is scheduled till Price Release.
The additional feature in CK40N is, If you have error logs, you will get a better picture in CK40N and not in CK11N
Additional Info: There is nothing that prevents you to run CK40N even for single material.
CK11N is used to create the cost estimate for a individual material. You can use this to create the cost estimate for any variant to be used but this will only create a cost estimate. Subsequently you will have to mark and release these estiamtes in CK24 to update in the material master so that you can use the same as the planned price for the materials.
Coming to CK40N, it is the costing run and you can schedule all the steps mentioned above, ie. cost estiamte creation, marking and releasing for all the material in a plant.
Suppose you have 1000 materials in a plant, no need to go to CK11N and create for the materials indivually, you can schedule all these jobs for creation, marking and releasing for all the 1000 materials as a background job.
This is the difference between CK11N and CK40N. There is nothing like which transaction is better. They are entirely used for difference purpose.