I have stageright in a EA stage 2 2004r and i use it all the time when racing/testing. Trans builder told me It's hard on the low roller clutch but it can take the abuse for awhile. You loose manual shifting in 1st gear selector and the car will roll a bit once it's set unless you hold the foot brake.
I like mine and I used it repeatedly for five years before the trans needed service.
To use it at least how I do in my car: pre stage in 2nd gear then bump into the stage beam until it's flicks or just lights up then I pull selector into first then release foot brake and let the car roll the rest of the way into the stage beam, go full throttle on the launch 2 step until my desired boost is reached then push or smack the shift selector into 2nd gear to release the brake and launch! I then shift into 3rd quickly so the 2-3 shift is auto.