I used to agree totally about the "out of control" Frenzy.
Of course, there is a lot less control. When in/under Frenzy, you may injure a comrade/get locked into the fugue of the fight-"nothing exists but the fight" attitude.
Saying that, IMO it has a lot less to do with mindless wild rage and more to do with total disregard for your own safety/well being (or others). More akin to a psychotic break.. It's not so much out of control, as just using your reptile brain; anyone up is a threat! Drop 'em all!
In the games I've been in, we have allowed players to use 2 weapons. The bad guys can too! But you still can't parry, no shield bonus, etc. The reasoning is... Once frenzied, the fist will likely be a tight ball. It's not like you're going to relax and drop anything on purpose. Why not let them use 2 weapons if they start Frenzy with 'em? What I wouldn't allow is the weapon to be changed for something else.(unless the crit says so) Too much higher brain, IMO. Not mindless but unpredictable, single minded drunk an entire 1/2 gallon o' whiskey rage. No weapon katas, combat styles or fancy moves.
In School, it just takes one prep round... I do think the difficulty is too easy to do for the benefits. And likely the character wouldn't even remember everything they did until they slept again. Then maybe, they would dream bits and pieces as though through unfamiliar eyes and in a blood red haze...