Stan releases are great for target shooting, provided that you are dedicated to shooting them correctly (i.e., with back tension).
All the new back-tension releases (regardless of compnay) are equally good when it comes to the mechanical aspects. The question is whether they fit your hand properly. For thumb releases, the Stan SX2 probably has the most adjustable thumb barrel, so you can make the release fit your hand not have your hand fit the release. Plus with the SX2, you can set the thumb pressure and thumb travel with an adjustment screw... no springs to change.