With the concussion grenades, be careful not to throw them right beside people, especially in enclosed buildings... The tend to fire at above 120 db or more. My Thunder B fires around 120db, and my buddy wanted me to test it out on him (he's insane...) Needless to say, it was in an open field, but it happened to land right beside his foot. After it went off he couldn't hear very well for about three hours he said. Sooo yeah. Be respectful to other players when using concussion grenades. A game isn't worth losing your hearing over, just as much as your eyes... Be respectful, be mindful, be responsible. It's all fun and games until someone gets seriously hurt.
On that note, yes, they are fun to use, add realism to the game, come in handy every once in a while.. but they still are dangerous if not used properly. Not to mention they hurt like hell if it goes off in your hand!