Prism diagonals can be a handy accessory when you are in a situation that requires more drawtube travel.
1.25" prisms have the shortest lightpath when compared to mirrors and a 2" prism lightpath falls between a 1.25"and 2" mirror. This can get you into focus without adapters or extension pieces.

The issue with using a prism is that if the telescope is not made for prism use it can actually degrade the views.

So how do you find out if a prism will work with your refractor? Keep reading and I will explain

Once you are set up use a mirror diagonal and a high power eyepiece, something that will get at least 50x per inch of aperture. You may need to use a barlow. A 6mm with 2x barlow will give 59x with a 102 f/7

Aim your telescope at a bright star and defocus inwards. Look at the first ring around the airy disk. If it has a red/ orange/ pink tint to it a prism will work with your telescope.
If the ring remains white then a prism will not work with your telescope.

Hopefully this quick test will save some people money.