In an urban setting with street lights, the XT11 has a nice strobe but it's more of an annoying "wtf are you flashing me for" kind of power.
To physically force someone to yield you'll need a wall of light something in the 2,000+ lumen range.
The JetBeam RRT-3 comes to mind. 1,950 lumens. Decent sized. Looks good.
eh...the RRT-3 would also work as a baton too, so its sure an option akin to the S18...but 600 lumens is a lot to strobe with (enough)
I like the RRT-3 in that scenario though...1950 is even better than 600 L.
The advantage of the Klarus over that S18 and RRT 3 is the one button hit to get the strobe on....vs the twist of the control rings on the other two...The XT11's UI is more suited to hitting the strobe...but really, an XT11 might be ok in your fist like a roll of quarters type weapon, or to "poke a DNA sample", but - baton-wise, I wouldn't bother. SO the XT11 hits the strobe better, and the RRT and S18 hit the perp better.
For the record - if considering a strobe -
ALL strobes are "WTF....", that's essentially ALL they do, no matter how many lumens...even 200 lumens can work on a night adjusted perp, etc....stobes are not tasers...ALL they do is make the perp hesitate, which gives you the chance to capitalize. Its just a flashing light...the lights going on/off rapidly confuse a person who is not EXPECTING it...and makes them hesitate. Some are more disorienting than others...the more regular the flashes for example, the faster a person adjusts to it, etc.
After a second or two (More for drunks, etc...) they get their bearings back, and can then start thinking about what to DO again. That means you have about a second to take control of the situation in whatever fashion makes sense in the context. People who are temporarily unsure of their options/what they are up against, are more likely to be overwhelmed by the swarming thoughts (The WTF part), and will be more likely to surrender rather than risk tangling with an unknown threat level. If you have a strobe, who knows what else you might have, etc....it LOOKS professional...maybe you are more dangerous than originally thought?
While they are considering that - you are ordering them to the ground, and, generally, they comply...as YOU seem confident that they should, and they don't really know yet...so they comply.
If you sit there doing a light show for one more second...they start to consider options..and you've lost the opportunity to direct them, they now have their OWN ideas, a different scenario (Hey, um, OK, there's a guy standing there with a light flashing at me...but that's it?...maybe I can rush him?" - etc)
THAT'S all a strobe is for...buying you time to take control...it doesn't incapacitate an attacker, etc...it just makes them say "WTF...." etc....buying you time.
If being attacked by an epileptic, people prone to cascade type migraines, etc...sure, the strobe might lay him out with a seizure, cause nausea/vomitting, etc...that does happen from time to time...but lets call that the exception.