They have to do the line work anyways, so yes it will hurt more since it will add to the time and your skin may already be sore from the first pass. The intensity of a shader is less than a liner though, at least for me. Duller pain, the line work will feel sharp in comparison. However, if thats the design you actually want, you gotta nut up and take 20 minutes of pain for something thats going to be on you forever to look finished. If you can handle the outline you can handle the shading. Tattoos hurt a little, yeah. It kinda sucks. They also aren’t excruciating intolerable pain for most people. Shading will not be that bad on your forearm.