This one seems to be a combination muzzle-brake and melee tip. However, there are other flash-hiders that also have spikes that are much less aggressive.
My concern with this particular model is that the individual tines may become bent... especially into the path of the bullet.
Here is a design by TROMIX... also a muzzle-brake. The tines/spikes seem much less likely to bend. Probably not horribly debilitating to be struck with it, but not the same as having a butterfly brush your cheek either.
I've seen some others online with little serated spikes somewhere between the two models pictured above. I've also seen some machined into a silencer, but that seems like a bad idea to me, since the torque on the threads would be severe in a 30 caliber-length can.
With the particular optics that I've got on my RFB (a 3-9x30 Nikon), I wouldn't want to use the top part of the weapon. I'm not nuts about using the buttstock in a smash either - even though gripping the area between the magwell and pistol grip seems awesome - because I feel like you're just aching to put undo sheering stress on the two captured pins that you have to remove to field stip the weapon.
Here is a "pistol bayonet knife" that attaches to the rail of most handguns. I suppose this could be attached to the quad-rail of the RFB. I have never handled one of these, and I wonder how well the mounting system works. I'd be concerned that a hard stab could twist it free... might only be good for one use. Still, I suppose its an option.
There aren't that many good surfaces on this weapon to use. In normal rifles, the whole of the butt-stock is an inert, non-functioning portion of the firearm, and relatively suitable for melee (for the most part). In normal rifles, the action is forward of the grip, and this necessarily means that the rifle barrel sticks out much more... it facilitates putting something sharp-and-pointy in an adversary's soft parts because s/he is an arm length from you when you have the weapon shouldered. Those features aren't really there in a bullpup.
Still... rather than being a nay-sayer who doesn't contribute to the thread (again).... there are a few ideas.