I have a Hadley Small Pro, and I can and do carry an iPad Pro fitted between the inner pouch and the back. (And why does *everything* have to be "Pro" these days...)
It is a very tight fit, and it makes the back of the Hadley rather more rigid than normal. I have the iPad inside a keyboard cover, so it is probably slightly thicker than a plain tablet.
The main downside is the weight. With the iPad, a camera and three lenses even the small Hadley is a bit of a pain to carry if you are out for several hours, as the weight will sit entirely on one shoulder. The upside is that it is very compact and meaningfully waterproof.