Autopens are very useful for high ranking officials who have to sign literally thousands of documents per year---but they have to be carefully controlled.
This is usually the job of the Executive Officer. The Secretary of the Navy usually has more than one Exec---probably about 4 officers --usually in the rank of 0-5 or 0-6 (Commander and Captain).
Autopens are large machines--about the size of a 1/2 or 1/4 a ping pong table. They are usually kept in a locked room and highly controlled so that they cannot be misued.
And they are not used on Silver Star citations -- I called and checked with someone who used to be an Exec to the AF Chief of Staff.
Autopens have shrunk over the years. The smallest I have seen were about three feet square and only a few inches thick. They were used to sign routine categories of documents and often several people had approval authority. I once had to impound the signature template from one because of embarrassing documents signed without explicit approval authority by the signer. However, the volume of correspondence forces a delegation to one or more trusted authorizers as long as the system is to require the major program head to sign the documents. Also, the actual operation of the machine is by a clerk or secretary. Thus, there are multiple points where a false or altered document could be signed by autopen.