Lock-off suspension fork
 

I know it's hard to understand why I ask this, I live in a country where decent rigid fork bikes are very rare.I recently found a way to attach rack to the suspension fork : Raider Front - Zéfal

If someone has a bike with a lock-off suspension fork and use it with these types of racks, It's not the same as the real rigid touring bikes ? (Apart from I know that moving parts can go wrong easier)
Or if I don't lock off the fork, and I load the rack on it, how does the bike handling?

I use a Tubus Swing rack on the front of my hard tail. This rack mounts above the shock and thus has no effect on the handling of the bike. OTOH, the rack you mention (as well as OMM and others) mounts below the shock and requires the shock to move the weight of the rack/panniers as well as the wheel which can't be good for it. Or, more strictly speaking, the shock is operating between the momentum average (mechanically speaking) between your wheel/rack/panniers and the (leveraged) weight of the rest of the bike on the front wheel system. If the shock is locked out, well, then its just like a rigid fork.

If at all possible, I'd suggest the former mounting system.

But presumably it does require that you adjust the fork preload, because the fork is now responsible for supporting the weight of everything in the panniers, correct?

as most suspension forks are all in the lower slider , and inside the stanchion tubes,

hanging panniers on the bottom increases the un sprung weight

adding mass to the wheel end of the fork

Tubus Swing as an alternative loads the fork crown, rather than the wheel, so the un-spring weight is not increased.

so the wheel will respond to hits quicker , as the mass is not increased with the pannier load added.

tubus - Swing

handicap is the variety of fork crown designs, which the rack's, clamps may not easily fit.

but the handling over rough ground should be better than if all the stuff is rattling up and down with the wheel ..

sstorkel: Correct. I pump it up so that I have acceptable travel when panniers are attached.
fietsbob: True. Getting the clamp to work on my (Fox F29) fork was a challenge, but ultimately doable. Lots of trial and error.