Body worn antennas (on vest) generally need to be tuned for the
band of interest due to the loading effects of the body. The bigger
issue is pattern, you want omni-directional but, no matter where the
antenna is put on the vest the body will be in the way for some direction.
On the vest also means potentially lower height and decreased range.
I agree with Allison that they may not be ideal for most
ham uses.
It might be worthwhile looking at how they are intended
to be used, and how that makes a difference.
The intended application appears to be military wideband
communication using spread spectrum over relatively
short ranges, when you may be focused on doing some
other task.
A ham equivalent might be chatting with your buddies
while digging through a pile of junk at a hamfest, or
communicating with the ground crew while working
on a tower, rather than hitting a distant repeater.
Most likely with the radio on your belt or in a pocket
where you might squeeze the PTT to transmit, but
aren’t picking it to talk on it.
The wideband SWR curve for the antenna (something
like 30 - 170 MHz, plus UHF) suggests some resistive
loading or other intentional losses. May not be an
issue at 100 yards, but likely significant at a mile.
Mounting it on a military vest probably puts a few
inches of Kevlar between it and your body, so less
detuning and absorption than a yellow safety vest.
The recommended installation is to run it up from
the radio, over the shoulder, and down the back,
which at least reduces the problems with body
blockage. And if your radio is also strapped to
the vest and not moved when you use it, the
feedline could be laced to the vest as well, so
it doesn’t get in the way.
Whether or not it makes for ham use depends on
individual circumstances, of course. I wouldn’t
count on it for reliable communications any further
than I can yell (and perhaps less - I’ve been
measured at 1/3 mile). But if it keeps me from
needing to shout and annoy everyone else
around me, that might be a good thing,
But since I’m not using wideband spread spectrum
modes, I’d probably try a 1/4 or 3/4 wave wire
woven into my yellow vest and pruned somewhat
to resonance when I’m wearing it, and see if that
serves the purpose at a lower cost.