Some guy had his vertical grip break off his lower rail and blew his hand off. Read here
https://www.thegunwriter.com/19139/another-devastating-kel-tec-ksg-injury/
I've also read that he was using an already-broken grip, but better safe than sorry IMO.
A whole lot of misinformation when you dig down thru the details.
The injuries
were predictably devastating.
The first guy's VFG slid off the front of the rail. The rail didn't break.
https://www.thegunwriter.com/17484/a-devastating-accident-with-the-kel-tec-ksg/
TWG said:
"The attorney cites the compact nature of the KSG, and the fact there is nothing on the rail to “prevent the grip from sliding off.”
They also noted alleged problems with the forward grip: “Nothing but a polymer nipple secures this grip to the rail — this nipple partially sheared off during first use.”
Clearly a problem with the grip, not the rail.
The second guy had his grip "break off of the rail".
https://www.thegunwriter.com/19139/another-devastating-kel-tec-ksg-injury/
It is unclear if the grip broke, was already broken, or the rail broke.
Matt Stanek of Kel-Tec said:
"Kel-Tec, he said, is not taking any “direct action” as a result of the injury.
He was unaware of any lawsuits filed against Kel-Tec stemming from any injuries with the KSG."
This speaks volumes. I'd say the grip broke.
All of pics of broken rails posted here were obviously not from shooting but from an extreme sideways force applied to the VFG on the rail.... like putting your foot on a long VFG and trying to unscrew the really-really-tight barrel nut with a wrench

.
The bottom rail is polymer not metal. If you want a metal one, add it.
I have yanked, tugged, jerked, and viciously-cycled mine with all my might for years to no ill effects. I believe along with KT and the grand lack of lawsuits, that there is nothing unsafe about the factory bottom rail. Accessories do need to be carefully mounted on it though, just like any other rail.