I had the shop apply Framesaver to both of my steel frames prior to picking up the frames, so no personal experience with the stuff. I could have easily done it too, but they didn’t charge extra, and also installed the headset cups, cut the steerer and chased/faced. The peace of mind knowing my frame is not being eaten away by rust on the inside is well worth it. If you do it yourself, try to keep it out of the BB. Pretty sure you wouldn’t want anything inside the frame when applying.