So for anyone wondering why more research has not been done in this area, this appears to be an unbiased paper with a decent method, on an interesting topic. It has had 5 citations in 4 years, in science terms that is tiny, and the research institute is not going to throw a lot of money at an area which has elicited so little scientific interest. I don't agree with this, but that i the reality.
Investigation of motorcyclist safety systems
contributions to prevent cervical spine injuries
using HUMOS model
From the discussion;
The three different safety systems technologies stud-
ied in this work did not show any major changes within
the whole cervical spine injury mechanisms except regard-
ing movement amplitudes. Hence, according to simulations
performed, neck brace systems investigated did not propose
a technological means to improving neck injury protection
by modifying injury mechanisms. The interactions with
thorax (or helmet) component were extremely important
regarding safety system capability to control joint kine-
matics. EVS and Leatt safety systems which are initially
well connected to thorax segment provide an optimal inter-
action with helmet component. On the opposite, Thuasne
neck brace with no fixation was free to move according
to the helmet kinematics and then followed the reference
kinematics without any influence on it.
As showed in Figure 16, the neck brace’s capability to
improve cervical spine safety could be postulated accord-
ing to both modification of joint kinematics (or delay for
bone potential failure) and on a shift of injury location from
proximal to distal cervical spine. Hence, as a synthesis, the
incidence of EVS and Leatt brace systems to modify kine-
matics and consequently injury risk level are summarised in
Figure 16. The results obtained showed a shift of injury risk
from the upper cervical spine to the lower cervical spine
which could be considered as a step towards reduction of
injury severity.
Basically what they have said here is if your going to break your neck a neck brace wont stop it, but it 'may' help turn a quadraplegic into a paraplegic, which is a good thing.
Also one of the data graphs shows the EVS brace appears to be slightly better than the Leatt overall, particularly for oblique (diagonal) frontal and rear impacts.
Conclusion
To our knowledge, this study is the first to present a com-
prehensive comparative analysis of cervical spine safety
systems regarding multi-directional impact conditions by
comparison to a reference simulation. The methodology
used in this work could be used as a basis for the evaluation
and optimisation of such safety systems toward, the defini-
tion of a global framework to evaluate efficiency of such
devices.
With the design of safety systems, the challenge could
be to keep the same injury mechanisms limiting joint ampli-
tudes or to modify injury mechanisms in order to shift injury
occurrence or location. With the current safety devices we
never showed any modification of injury mechanisms or
important modification of joint amplitudes.
With the same behaviour as the reference simulation,
soft safety device tested did not show any efficiency. EVS
and Leatt brace have a contribution to neck safety with
slight modification of rotation amplitude and a shift of upper
cervical spine injury to middle cervical spine injury. These
results could be considered as a step towards the reduction
of injury severity of such safety devices. At least, an optimal
interaction with thorax and helmet obtained with Leatt and
EVS safety system was reported as an important feature to
support more efficient safety devices.
So they are saying that they essentially don't work and research like this is needed to help improve the efficiency (ensure they actually do what they are meant to do) of such devices.
Hence, my statement on page one of thread has been validated, there is no evidence that they work (but, they 'may' work?).
The paper has 11 pages and lots of graphs, can post more if requested.