decent in arena, unplayable in constructed. It's on par with venomancer in arena which is about average, this might be slightly better since the taunt helps you live and 1 attack vs 2 attack poisonous is pretty much the same thing.
It seems like 5 mana is a common choice for Blizzard when they make a card specifically designed to just kill a minion, like Assassinate, Lesser Onyx Spellstone, Vilespine Slayer and Vilebrood Skitterer. The Trogg here seems to fit the theme a bit with Taunt as the idea would be that your opponent needs to slam a minion with 5+ attack into it, sacrificing that minion. The Trogg is usually bad though since it gives your opponent some control as to how to deal with it. Also the fact that it can be countered by divine shield, strong weapons, removal spells... and Cabal Shadowpriest hurts too.
not in the "double silence in every aggro/tempo/midrange deck meta." it's a lot more like a 5 mana 1/5. tar creeper and rotten applebaum are way better defensive options and aren't as big a tempo loss if they get silenced.