I currently have the diadema pseudochromis, which is in the same family and he is a little terror, he has kept my 3 green chromis, six line wrasse and diamond goby to one side of the tank. He also attacks my shrimp, and Im sure if I got in the tank he would attack me too. He did this all in less than 12 hours. He's fairly small too, so in this case size doesn't matter.
I just picked up a Canary Blenny, not a Canary Wrasse as pictured above and hes one of my favorites already. He swims with a slight arch, pointing downwards towards the sand and LR, in search for food I can only assume. He will not actively go and attack anyone, injecting them with venom, only when he gets swallowed by...say, an Angler or a Lionfish will he bite back. His venom is a defense mechanism, not an offensive strike. If I were you, I'll pick one up without hesitation.
On a side note, he rests in between my Seio powerhead and the plate that holds the suction cups. Its funny because when I first got him, he darted upwards to the tank when the lights went out and vanished. I thought "oh no, not another jumper, but low and behold he hid between the little area where the Seio is connected to the Glass sunction plate. Every single night he swims up there and lays down to rest, very amusing.
Oh yea, he has only started to take interest in the food I feed. He'll be fine if you have LR and LS. Mine is FAT which makes him look PHAT, one of the better looking blennies in my opinion.
The pseudochromis or the canary blenny? Because if you read the replies over again the only "problem" with the canary blenny is that they have venomous fangs, but as I stated above, its a defense mechanism and not an offensive weapon.