A Newton meter is just any device that measures force (it's called a "Newton meter" because a "Newton" is a unit of force). A spring balance is a device that measures force by measuring how much a string stretches when a force is applied to it. So, a spring balance is actually a type of Newton meter. There can be other types of Newton meters, too: for example, there are devices called piezoelectric sensors which generate a voltage when a force is applied to them. By measuring the voltage generated, it's possible to measure the force applied to the sensor.

In short, a spring balance is just a type of Newton meter.

A Newton meter is a unit of torque, which is a form of work or energy; in other words it is a unit of measurement. We use different units to describe amounts of different physical quantities. Some examples to help you think about it: we can measure temperature in Farenheit or Centigrade; we can measure distances in feet or meters, we can measure mass in pounds or kilograms. These are all different types of "units." On the other hand, a spring balance is an instrument that measures how much mass an object has. I hope this helps.

A Newton is a unit of force, like a pound (we think of pounds as units of weight, but really they're units of force; weight is just the force exerted by gravity).

I don't know what units the spring balance measures force in. If it measures force in Newtons, then it seems to me that they would be the same thing. If it measures force in pounds, then they're different because a pound is a different amount of force than a Newton.