My two cents: The cost of these things ($47 each) is ridiculous compared to what you actually get.
I think I would rather spend my money on reloading supplies.
But, If you think you really need to have something like this you would be better off buying a surplus of fireworks on July 4th and making a few dozen sparkler bombs.
Are they going to be as easy to detonate as a grenade? No.
Are they going to be comparable to 127 decibels? Depends.
Do your research and go easy. Don’t be the idiot who creates a stick of dynamite and then blows off his hand.
Seriously, sparkler bombs are no joke, But if you want a cheap “Distraction Device” they will definitely get somebody’s attention and if discharged in a confined space have similar effects as a flashbang.
Redneck Ingenuity 101.