I have a Davidson barrel vise (Viper's is the same design) and it works but you have got to have it tight tight to make sure the barrel doesn't spin. Also, it will mark cerokote. I use it the same as MLN with using a toilet paper roll.
I've got 6-8 different rear action wrenches I've bought over the years for different actions I've owned.
If I was doing it all over from fresh…I'd buy the SAC modular, just for simplicity and storage if nothing else.
I did buy the cheaper of the two SAC barrel vises they have…because I needed something that wouldn't mark cerokote. It grips much better than the Davidson without leaving marks.