Easiest way to test shock absorbers without shaker plates is to look at the top of the shock where the rod comes out. If there is oil on it, you need to change it. Next step is press hard on each corner of the car and bounce it up and down 4/5 times. A bad shock will keep bouncing after you stop pushing it up and down, a good one won’t bounce.
For any suspension upgrade or repair, you need to decide and share on this basic question first:
Only for off-road
Only for Tarmac
Mix usage - daily driver + weekend off-road