Your advice seems a little unusual; perhaps you've had caring line managers in the past, but in my experience, the less they know about your grievances the better. If you suggest you are unhappy, your manager is likely to assume you are looking around anyway. Thus you end up giving your manager the upper hand in negotiations. If you don't have a back up offer in place, you are simply hoping that your manager is a nice person who deals with your issues fairly - but there is always a very significant chance your boss reacts badly to your dissatisfaction. Then where do you go without a backup?