The only stupid question is the one that isn't asked.
An IPR heats the paint via infrared radiation (IR), whereas the heat gun heats the paint using convection (hot air in motion). IR and convection are two of three ways that heat can be transferred. IR is similar to how the sun heats the earth. When you're standing in the window on a cold winter day, you can feel your skin warming in the sun, even though the space between you and the sun is cold. The energy is being transferred directly from the sun to you without heating the space in between. An IR paint remover works the same way. The quartz rods throw off IR rays. Only what's exposed to the rays absorbs IR energy and heats. Anything shaded remains cool. This substantially reduces the risk of fire. With a heat gun, you blow very hot air onto the paint. The air can blow into cracks, carrying cinders or igniting something in the crack. Dust, dry leaves, powdery wood, are all very flammable.
Quartz rods are not very efficient producers of IR. Much of the energy the quartz rods receive from the power cord is not converted to IR. Quartz rods glow red, the light is energy wasted. Some is also conducted to the air surrounding the rods. The efficiency of quartz is about 50-65%. Even so, quartz is adequate for heaters and IPRs. Ceramic has a higher efficiciency, close to 95%. The ceramic IPR doesn't glow.
Another advantage of an IPR over a heat gun is that second for second of exposure time, the IPR doesn't heat the paint as hot as a heat gun. Therefore it is easier to work safer with an IPR in regard to lead outgassing from the paint.
Another advantage of an IPR is that you can heat and strip a larger area than a heat gun