Big thank you to NFStrike.com for sending over a sample of their "Water Ball Grenade" - a toy that at first glance uses water ball beads (akin to Xploderz and Vapor ammo) to spray out on impact. Fun fact, their "grenade" also works well with Rival ammo (and apparently Mega darts too?)
It's of a serious quality plastic build, the springs that flip the launch doors out are pretty beefy, and it looks like these can take a drop on a concrete floor (seen a video by Jodo Cast also that looks inside a warehouse and the thing didn't break, either way these things are supposedly built pretty tough.)
It works like you would think a "grenade" would work - after loading, you insert the pin to keep everything together. When going to throw, pull the pin, toss, and watch the fun. There's a piece inside that moves around to release the doors, and flip everything out every which way. For best results you really do need a strong impact, soft tosses didn't seem to have as much magic as tosses (high lobs) that allowed more speed and impact.
The price nowadays seems pretty reasonable, and I think from the moment they said they would ship the product arrived in about two weeks (feel free to chime in in the comments if your shipping experience is different!)
The only real misgivings I have about the toy are at how at a quick glance (even with the orange trim) these might be mistaken for something more realistic if left behind. If I were to use these it would be in an arena, an indoor scenario, something that would reduce the need to pitch overhand and reduce probability of losing the toy. And even then, I still wouldn't feel too comfortable throwing these without being careful, or trust people to not get caught in the moment and accidentally throw the toy at someone and not near them for blast radius results. The pin is a small piece of metal and may also get lost, including a spare would go a long way, otherwise make sure to find some way to flag yours in case you throw it or drop it.
HOWEVER, considering the previous available incarnation of foam dart grenades was lackluster at best, this is a serious improvement over time! If anything, these are hilarious to keep around and fun to toss, just be careful of the people and players around you. The pricing is pretty reasonable with other accessories and blasters so definitely a "worth a try".