Disclaimer - eric shahn (as he always puts his name in lower case) is a budo bud of mine in Japan.
It's funny you the word 'decent'. That police manual is straightforward- it is not high literature, it's a policeman writing for other policemen.
Sometimes he does insert humourous or curious, informal notes, but the translations are 100% serious. As you said, he's not an academic but rather a very talented amateur researcher. I've asked him about some of the footnotes and he'll shrug his shoulders, just say 'it's what I thought about it.'
He is brilliant at these translations. He's translated about twenty books covering a range of subjects and self publishes at very reasonable prices. And has more coming as he does projects in parallel. He makes these often very obscure but very interesting books available to a global audience. I follow him on Facebook and don't think I've ever seen a negative comment, but many many complements.
There's not much money in it for him as he keeps the prices low, and some have limited appeal, but they provide insights into aspects of Japanese martial arts that even modern Japanese have difficulty finding. Even very few Japanese can read them, much less have the deep and broad martial arts background of Eric to make good, practical translations that modern Western martial arts fans can read and appreciate.
Beyond deciphering those very difficult to read old texts, he also does the entire layout, artwork, etc. it really is impressive.
Also, he always publishes the orignal text along his translation, so anyone can try their hand at a better version. My money is on Eric. The more he learns the faster he goes.
I highly recommend them. I have a dozen or more myself.