If that is not a legally owned Glock 18, or if they are not part of some government sanctioned agency... big illegalities there.
1. foreward grip on a handgun - illegal
2. full auto on a handgun - illegal
But legalities aside, Here's some tips to remember when shooting handguns if you want to keep all your fingers.
1. DO NOT place your supporting hand anywhere near the muzzle. That includes balling your fist and using your left wrist as a support; trying to hold your gun as if it was a rifle, cupping your hand around the muzzle end of the frame; holding your frame and slide in left hand and shooting from the hip. I've see it all.
2. DO NOT let any part of your hands come in contact with the slide. There are people who like to hook a finger around the trigger guard, then put their thumb on the slide. same goes for sticking leaving your thumbs in the path of the recoiling slide.
3. When using the slide release to chamber a round, EXPECT the gun to go bang even though it is not supposed to. Anyone remember BamBam31's Makarov that went full auto? And left a hole in his left hand? Keep your supporting hand out of the line of fire if the gun goes bang. Slam fires happen.
4. DO NOT pick up rounds off the ground at the range and say to yourself, "Lookee here, I gots me some free ammo!" You WILL pick up some idiot's overcharged round designed to be fired in a TC with half-inch thick chamber walls. It WILL blow up your gun and, if you are exceptionally unlucky, part of your hand as well.
5. When shooting a revolver, DO NOT allow any part of your body be covered by any part of the cylinder. Enough conscripts lost their fingers to escaped gas during the turn of the last century that the Russian military required their 7.62 Nagant pistol to have a gas-sealing cylinder design. Like spring loaded firing pins, this is another Russian safety feature that seems to have been discarded in favor of idiocies like magazine disconnects and integrated child locks. If you put your left thumb in front of the cylinder of, say, a S&W 500, you WILL blow off part of your thumb. That gas is superheated and escaping at high velocity. Your skin is no match for it.
Now rifles, that's another subject. But enough for today.