I put the complete Apex Tactical trigger kit in my Shield. It is a definite improvement over the stock trigger. The Apex trigger kit eliminates the rough take up that I had on my gun, and also gives you a very nice clean break.
Its not the easiest trigger kit to install, since it requires the removal of the rear sight to do the complete kit, but I think most guys could do it themselves if you have the right tools. A sight drifter is a big help if you have one.