For a weak economy IMHO the Euro is worth the disadvantages (and I happen not to consider the inability to do competitive devaluations a disadvantage). These can be small (GR) or large (IT) economies. For a pretty solid (sometimes strong, sometimes less strong, but never "weak") economy (DE, NL, FR, etc) it's definitely good; the small amount you lose in freedom of action is far overshadowed by the benefits (who did better from the greek financial crisis: Greece or Germany?). But for a middling economy which I consider the UK to be, despite its large size, being coupled to the eurozone would give them the worst of both worlds.
BTW I don't think this is an argument for the UK getting out of the EU; I think they should fix their shit (which goes back decades) instead.