I've read some of his stuff on the asubhasannam training & progression. It's pretty good/interesting. Title is "Samadhi begets wisdom" or something like this.
I've also read excerpts from his other book, that about Ajahn Mun. That one makes me think that the author, if he himself believes those things, at the time of writing, is quite certainly not Ariya.
I think he is probably an accomplished yogi in general tho. Maybe like Alara Kalama or Uddaka Ramaputta attainments & views.
That book i recommended is pretty shocking, it's hard to imagine what life was like for ven. maha bowas and of his monks.
Another thing is that sometimes he seemed somewhat cruel, like on occasion he said some things about children as being just out of hell. The way he carried himself in general from what i've seen has been less impressing, chewing tobbacco, crying, harshly complaining about children.
I've heard he said once to fill a new meditation house that was done built, knee deep, with excrement.
Im sure some might think these are eccentrisities of an Ariya but i see nothing of this sort in the Sutta Pitaka nor Jataka.
This is my impression.