ones that actually blow up and blow shit everywhere are effective anywhere.. in or outdoor...they work a lot like real ones, they're fucking loud so they scare the shit out of people so they sissy out when one lands in their foxhole.
Tornado grenades are useless outdoors because they usually hang up on something and only shoot BBs in one direction. Indoors they can free roll and spread which is what makes them effective.
Nothing like throwing an explosive device into an enclosed area and hearing "OH FUCK" and watching people bail out.
If game organizers allow real explosive devices on the field, it should be part of the morning safety briefing on their safe handling.. IE don't cook them or throw them back. Ear protection also recommended.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.