"How does a VLFS (variable level float switch) or a wired float switch work?"
The pumps that come with a variable level float switch are non-automatic pumps. You just attach the float switch and the pump will behave like an automatic pump. However, the VLFS allows you to specify the water level (between 6" and 36") that will turn on/off your pump. This is different than the normal automatic pumps that have a preset water level that turns them on and off. Since the VLFS is detachable, the pump can also be used as a non-automatic pump.

"What's the difference between an automatic and non-automatic pump?"
An automatic pump has a built in float switch that will turn on the pump automatically at a fixed water level. After the water is pumped out to certain water level (also a preset level), the pump will turn itself off. A non-automatic pump has to be manually turned on and off, or with a separate control like a piggyback float switch.

"What is a vortex impeller and what does it do?"
A vortex impeller handles debris better than other impellers, therefore, helps to prevent the pump from clogging. Below is an example of a vortex impeller.

"What does the automatic reset thermal overload protection do?"
If the pump gets too hot the thermal overload protection will turn it off until the pump cools down (to prevent damage to the motor). The pump turns back on after it has cooled down enough. This backup protection feature is useful if some debris causes the pump to overheat.

"What does it mean by 'dewatering'?"
The pumps are called dewatering pumps because they are made to remove water and pump it somewhere else.

"What's the advantage of a double seal over a single seal pump?"
The inside seal provides added protection in case the primary seal should ever fail.

"Why is it called a submersible pump?"
These pumps are designed to be placed directly in the water. They draw the water up from the bottom of the pump.