Ours are removable, set up on shock cords off the rig except when dousing the main. This gets away from most of the hassle during raising the main and also allows use of a conventional mainsail cover.
We primarily use them to prevent the main from dropping all over the dodger and scratching the ($$$) lexan windows.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"