When I put mine on I felt like I got better throttle response. Was it day and night...No....but I felt like it was better than before. HP gains....maybe but you're probably not going to really feel 5 hp in the butt dyno.
Would I buy it again....definitely. For the money I felt it was worth it. Now, if you're needing the money for other mods like maybe cradle bushings or something that you will feel day and night difference then you might spend the money there first but eventually I would say pull the trigger and get one.
Here is the visual difference between stock and VMax. You can see how it's smoothed out with swirls and some of the metal has been removed to make for better flow. BTW, this was a used one.
2SS | M6 | VR w/White Stripes | 1 3/4" KOOKS - 3" Magnaflow | LPE 3.91 gears | ADM tuned | Halltech w/ADM Scoop | Spohn/BMR Trailing Arm/Toe Rod | BC Coilovers| Pedders FE4 ZL1 swaybars | Cradle/Diff/Radius Rod bushings | VMax TB | Morimoto Projectors | MGW shifter | Red Calipers