We actually done this "straight arm" design way back a few years ago.
The problem with this design is while the "theory" checks out, what happen in real world application is very different.
What we had found is this straight arms design make the EP3 / DC5 steering "jerk" under power when combined with LSD.
The initial test with EP3 was fine, but UK spec do not have LSD as standard.
A certain amount of DC5 did not have any problem either.
As the steering arms are attached to the damper, the camber and toe are linked making it very difficult to locate the issue.
As for why Seeker use this design, it is possible that they do not have to worry about this as majority of their customers are track car.
For most of our customers who use their car as their daily / fast road / occasional track cars, all type of road surfaces have to be considered.
In the end, we discontinued this "straight" arm design because it seems the standard "curved" arms are less prone to this effect.
And if the customer feel the need to install extended track rod end or steering rack spacers, they can also do so.
We also have look into the "reverse taper" that are on the Mugen suspension, but we also have feedback of a similar issue as the straight arm so we decided against it also.
As far as bump steer are concern, we actually measure up an EP3 race car about a year back and found the geometry of the steering arms are fine with the track rod in the standard position.
Of course this depends on ride height and so on, but in that car we didn't have any problem.
That is my experience with this, so I would steer away from the straight steering arm design (pun intended).
We just can't find a good reason to use it as it isn't good on road cars base on customer feedback, and it isn't great on race car based on our measurement as well as experience.
Jerrick