Our Facet pump works fine on its side.
Also lets the engine pull fuel through when off
We installe dit on engin supplier recommendation but find it is unnecessary to lift our fuel about 3 ft with an empty tank
It is great for refilling the fuel filter when changing elements

Our Espar works fin without a feed pump BUT it is hard to get all the aire out of the lines after working on system
I disconnect the tiny fuel line at the heater, disconnect the pump, then activate the pump by touch and release of 12 volts to the contacts until clean fuel flows. may take a few hundred strokes.
Recommended approach is t have a dedicated connection t the fuel tank with only the tiny Espar line. Makes sense to me, but we have not done it.