I have an older model of the M203, and also a Soviet AK type.
To be honest they have very little practicality.
I have made more use of them for just making noise for fun.
To be of any use you need multiple shells and they are all single shot unless you carry a bottle of green gas, or CO2 to recharge them.
If the game has some relevance to the shells such as simulating blowing up an object, destroying a vehicle etc then there is some form of use. But depending on the shell you just have a small single shot shotgun style blast
40mm launchers have been used in the US to fire the Nerf type of rockets - and have had a rule with regard to special vehicles or objects, but they still have little power as you’re blowing green gas/co2 into a foam shell to blow it out of the barrel. You’d get better performance throwing it
My M203 is the long barrel type similar to the video which could launch a nerf, There is also a short barrel type that can’t launch a nerf and my AK launcher is also short so couldn’t launch a nerf
Without a specific use they are a heavy piece of metal hanging off your barrel and a drain of £