Ok, I received the artifact "Dark Ring Thruster" "special"
at size 12 defense 70 it doesn't seem worthwhile to install given what I have access to at rank 117.
Is this a specific defense part to be install when fighting the dark ring and then un-installed?

No. It is just defense 70 like researched defense modules do. It doesn't give special benefit against NPC..

Dark Ring Thrusters are just good extension to your maxed 4 defense modules..

You must've researched rather far up the defensive tree if the Dark Ring Thruster "doesn't seem worthwhile". It gives you almost 6 defense (5.8) for every 1 deck, Phase Shift Engine Mk. 3 (45k x 3 research IIRC) gives 4.3.

What defensive technology do you have that's better?

Special Tech modules (ones that come from NPCs and missions) have seperate limits than normal modules. (in other words, they stack) For example, even if a player has all 4 thrusters equiped, they can still equip a Dark Ring Thruster.

I currently use Microwarp Nacelle - Mark III
Defense +204 at space of 54 so it isn't as good as 70/12 but I didn't realize that it wouldn't count as one of my thrusters. I'll be sure to install it.
Rank 117

i have 4 installed instead of one of the larger modules. 48 vs 64 space and 280 vs 266 def. the clear winner is the thrusters!
im comparing 1x Phase Shift Engine - Mark III to 4x thrusters.