Information in this thread will mainly be about Koni vs Tokico, but you can use this thread for references to see Tokico vs OEM
As widely known Koni Yellow are adjustable shocks with lifetime warranty from manufacturer.
I can report that warranty is legit as I got a chance to use it even before I installed my shocks.
One of the shocks came in with a defect and had to be replaced. For some reason vendor that sold those to me did not feel like they are the ones responsible for replacing defected item that they shipped, so I had to go through Koni warranty.
Some concerns right off the bat. When I got a replacement shock for one of the defected shocks, while trying to compare the rebound rate with other shock one of the shocks would rebound faster (piston rod would come out quicker after compressed from one shock). Koni tech support told me it's normal and I should not worry about that. So I installed it the way it was. So far I do not notice any issues. Car seems to be leveled and shocks work fine on both sides.
So on to the comparison:
Koni body is tiny bit taller and piston rod is also much longer, but if you look at the spring plate seat you'll notice that they are at a very close height. As I mentioned in Tokico vs OEM thread I did not need to use a spring compressor to put on the springs. There is hardly any spring compression required (Tein H-tech springs) when installing these shocks. The thread portion of the piston rod is much longer and on top of it is adjustment valve. I'm guessing it's designed in such way to make it easier to access the adjustment valve.
Another good thing of Koni shocks is that mounting fork has a nut already built it.
Not much difference there besides the mounting bracket. This time Tokico has built in nut and Koni does not.
Don't mind the shorter Koni, it's not extended all the way. Koni has a built in plastic dust shield, Tokico has removable rubber one (currently removed in the picture).
It was my biggest concern. I was not sure what will it take to adjust these shocks and what would be involved. Turns out that they can be adjusted on the fly. Meaning that piston could be in any position; all the way up, all the way down or in the middle. It could be adjusted at any position. Front shocks are accessible under the hood, adjusting valve is located in the center of the piston rod and could be adjusted with a **** provided by Koni. Simply slip it on and turn it.
For rears car needs to be jacked up and adjustment is done at the top of the shock with a nail or a small hex key. You simply put it in the hole and rotate the valve left or right.
In the picture my car is jacked up and shiny area at the top of the shock is where the adjustment is done. You can see there is quite allot of room between the tire and fender. You can easily slip your arm in there and do the adjustment. Obviously with larger wheels (I got 19s) you would have less space there.
Overall I quite like them. All of the reviews on the net say that they last quite long with lowered springs, and could be easily rebuilt or exchanged under warranty if they go out. That was my main reason for getting Koni. I have them currently set on the softest settings and they provide enough bump absorption while still giving stiff and sporty feel. Difference between full soft and full firm settings is quite significant.