Buy the Greddy unit. I like mine a lot for three reasons:
1. With the Greddy turned "off" I still have stock boost and the unit will show me my boost pressure.
2. The Greddy has two settings, a LOW and a HIGH. I can move between these two settings by pushing a simple little button. Plus, I can program each of these settings to perform individually.
3. The Greddy unit does not spike. You set it and it goes to that point. No drama, nothing. The thing just works like it is supose to. Also, it does not have a stupid LCD screen that you have to mount some where.
3a. I like Greddy's products (their fit and finish is great) and the boost controller, along with my turbo timer, come with a year long warranty.
Hope this helps.