The safeguard was designed to be a rappel device, which includes lowering a climber. The lowering part is pretty much just a switched around rappel.
I’m the one who brought up the warning from Mad Rock originally. I’ll see if I still have the picture of the warning. IF not, search my threads and you can find it.
If you read the paperwork carefully from Mad Rock, the warning against any sort of friction knot below the safeguard is that it can cause a shock on the Safeguard. As a belay device it is actually designed to allow a slight amount of slipping when a climber falls and the device grabs. This very minimal slipping as the device grabs the rope helps to cushion the device and the climber a bit. You would be amazed the amount of force a falling climber can generate. If you have a friction hitch or other device below the safeguard then you get a more sudden jolt on the device which could damage the device.
With any sort of mechanical belay/rappel device, there is a huge learning curve to trust the device. It will hold you, as long as you don’t panic and grab it wrong. That takes familiarity and practice. The Safeguard is a great device that works beautifully. It will easily hold you, especially in the applications we use it for.