The red dot finder is quite sufficient with a telescope that has an 80mm aperture. It is quite easy-to-use. It proves to be very useful most of the time. Also since you will use Meade Infinity 80 at low powers, the telescope itself will act like a finderscope.
The included Barlow lens will double the magnification with any eyepiece. For example, if you are using the 26mm eyepiece, your magnification will double from 15x to 30x. But unfortunately, the Barlow is not very useful with Meade Infinity 80. You won’t go up to really high magnifications anyway and if you are, you are probably better off using a low aperture good quality eyepiece.
The 90-degree prism is quite useful for terrestrial viewing. It corrects images’ rotation and saves you from bending over all the time. But it dims the image and creates diffraction spikes on bright objects. Therefore it is not very useful for celestials.