Personally I would say most are far from ideal, which means they aren't going to be anywhere near efficient as they might have been.
Short draw, sinew backing would mean they were safe and relatively durable, I'm sure they could bring in meat, so they would have met the expectations of their owners.
Another good comment. It's hard to tell from the dark grainy photos but I see evidence of hinging and unevenness in the bows. Yet bows of this sort killed many a four and two legged animal.
Quotes from an historical era Indian about bows:
"Four arrows was the regular allowance for the
killing of one buffalo during a horseback chase. The
need of more than that number was discreditable to
the skill of the bowman. Less than that was a matter
for boasting. If one killed a buffalo with only one
arrow, that was wonderful. "
"
We camped near one certain big town far along on
our journey. None of us were allowed to go into the
town, but I went walking all about the outside of
it to look at it. As I walked I found a big piece of
wood that I wanted. I had seen at past times this
same kind of wood, and I knew its usefulness to us.
It was the heavy piece that lays across the necks of
cattle when they draw a wagon. The Indians liked
to get these, because they made the best kind of bows
and arrows. I picked it up and lifted it over a
shoulder I went right away to my home tent lodge.
I made a good bow. My mother had in her packs
some dried sinew from buffalo back tendons. This
I used to string my bow. I made then ten arrows.
I got here and there some pieces of metal for the
points. My mother made a pouch for the bow and
arrows. She made it of a calfskin she had tanned as
we were moving. I was glad now, with the full
pouch slung from my shoulder and dangling at my
left side. Two days I spent most of our camping
time at this work. "
