To each his own. I carry a sig p365 + 1 extra mag in summer, G19 + 1 extra mag in winter (both mags are 15 rounders). Plus 2 knives. I think an extra mag is important. I've had the base plate fall out of one during a competition. Would hate for that to happen in a SD situation without a spare.
I'm in the same boat. I just bought a PRS rifle and this will be my first time mounting a scope. I bought this tool to assist. It's not cheap but I imagine I'll need to mount a scope or two in the future, and I prefer to do things myself whenever possible.