If you had a solid tube Mk2 - or better still, a Mk5 Sten and 10 good magazines the worked in YOUR gun, that was all you needed. It was as safe as the other SMG's too. In that fired when you wanted it to and wouldn't fire when you didn't want it to, contrary to some ill informed writings.
But If I had to carry one in action again, it'd be a trusty L2A3 Sterling. The Rolls Royce of SMG's