I was looking on joeboboutfitters.com and saw this J&R Research Triger Adjuster
How does this reduce triger pull and shorten creep?
Would this be worth the money?

Looks like it has a longer set screw inside a hollowed out grip screw. If your grip screw hole goes all the way into the floor of your lower, the internal extension will come up and restrict the motion of the trigger. It is described as adjusting the pre-travel on your trigger. This means it will come up under the trigger's tail and bring the resting position of the trigger nose (sear) closer to the release point. The odd tool pictured is an extended bit to let you adjust it through the bottom of the grip

Here you can clearly see the grip screw "bore" and how "up pressure" from this point would affect trigger break.

save your money. $35 + shipping,,,forget that.

things you need,
#1..shortened grip screw.  if you have an after market grip you may already have a short grip screw. I know the Moe grip screw work for this!

#2..1/4x28  tap. forgot what I payed for this but it was just a few dollars.

blue loctite.

and go here.
http://www.junkyardgenius.com/firearms/ar-15/ar08.html

I did this and added a JP yellow reduced trigger spring and the JP red heavy hammer spring  (JP's enhanced trigger kit $15-$19).
ended up with a 4lb trigger pull and almost no creep.  but keep in mind this mod does nothing for the trigger reset travel!!  

in total this mod cost me around the same price as what joebob is selling.  but its way more then what you get from joebob for the money!

This is great for some people.
Others might want the luxury of being able to tweek the setting with the grip in place.

There was a machinist/member on Maryland Shooters that was selling the deluxe kit for about $18.

+1 on adding the springs.

If you drill the grip screw for the allen wrench it's $1 DIY mod.  Works great with the oem single stage triggers and two stage triggers.  While your in there doing a DIY you can drill & tap a second hole under the take down pin and add a adjustable set screw to tighten the upper fit.

The J&L is a bit pricey honestly. We sell a house branded trigger adjuster that has the grip screw tapped to receive the trigger adjuster screw inside of it, rather than in front of it. You can adjust the trigger without removing the grip screw. They're only $17.95, with the wrench. IMO, it's a much better option than tinkering with a screw in FRONT of the grip screw, as you generally have to remove the grip screw to adjust your trigger.  That is unless you drill out the grip screw to allow a long allen wrench to go through it.