The Transparent Viewmodel customization should't be used with a dxlevel lower than 90.
dxlevel 80/81 doesn't support the refract material, which mostly means that if you enable this customization, your screen will simply turn white!

If you're having problems, you might want to edit your fps config so that certain console commands don't disable your viewmodels' transparency:

mat_motion_blur_enabled 1 			//the only sure-fire way to keep refract masking on
mat_motion_blur_strength 0 			//effectively disables motion blur, personal choice + motion blur gets masked and looks bad with refract masking
mat_disable_bloom 1 				//disables bloom so refract masking doesn't create a dark rectangle over light materials
mat_hdr_level 0
mat_colcorrection_disableentities 1
mat_colorcorrection 0