Is it useful?
It jiggles?

Yes they do.You can do a couple things.One is to replace the spring that oposses the elevation button.You couls also buy a para sight from DS Arms. There are people making improved FAL rear sights.Is your L1A1 a real inch upper or is it a metric made by Century?

ummm it's an inch kit.  uses metric mags.  century L1A1.  

I believe those are metric cut for inch parts, mag well, charging handle, and top cover.  Where is it loose and are you talking about the front sight or rear.  All inch cut mag wells will take metric mags it dosen't work the other way.  If you are speaking of the rear sight, then if it is the dovetail cut in the lower receiver you can peen it in a little and then reinstall the rear sight.  That should take up the slack, if it is the apature then stick it in a vise and slowly squeeze it until you get it to fit on snugly.  You don't want it so tight it won't move.  If it is the front sight post then you may want to get one of those spring over things that tightens worn threads, if it is your front sight gas block then you have some more involved problems there.  Also. on the front sight post you my want to follow the threads with a tap, and tighten the front sight retaining screw.  If you have anymore questions feel free to ask.

I still don't get it... are tehse supposed to be primary sights and if so why do they flip down so easily???

and this is the rear site of an inch l1a1 from century.  takes metric mags.

Quoted: I still don't get it... are tehse supposed to be primary sights and if so why do they flip down so easily??? and this is the rear site of an inch l1a1 from century.  takes metric mags.

The "fold-down" rear sight is Indian, which isn't really inch or metric, but is highly sought after.

All inch sights fold down.  Australian, Canadian, British, etc.  They fold out of the way for the Trilux SUIT scope.  It can also be used to fold out of the way of a conventional scope as a side benifit.  They are primary sights, they just also fold out of the way.  

Most FAL sights wiggle around some.  The Metric sights are usually the worst once they get worn.  The rear sight on your rifle is held in place by a detent/spring arrangment that actually keeps the rear stight from movign around too much.  It also allows you to make range adjustments by just sliding the rear sight up and down the range markings.  If your rear sight is moving around a bunch, then it could simply be worn out (the rails are worn), or the spring could be weak.  Inch sights in good condition don't wiggle.

Inch sights are also "high" in profile.  Metric sights come in "high" (like the Israeli, or very early FALs) or "low" (like the G1, or SAR-48).  A compatible height front sight block needs to be on the rifle, so make sure you stick to either inch or a "high" metric rear sight.  

A good path to take is to put a scope on it and just use the sights you have now as back-up flip sights.

Ross