Hi,
Latching the striker over the rear of the receiver is a very positive safety. It not only locks the striker, but also locks the bolt shut. Soviet and Finnish soldiers were taught to use it as such. Nor is it the only rifle to use such a design. The Swiss k11/Gew11 and K31 use a similar design. And I had a single-shot .22 as a child that used exactly the design as the Mosin for a safety. And I have seen several .22's with the same design.
It can be a pain in the butt to operate a Mosin safety. I have seen and even tried several modifications myself. The difficulty in operation is directly effected by how heavy the firing pin spring is. You can carefully clip a bit off to lighten the stiffness. This can sometimes cause miss-fires with old hard military primers. I have also fashioned a steel loop and TIG'ed to the knob to give a better grip ala K31.
A good technique I've taught a few 91/30 shooters is to lay the buttstock along the length of the inside of your forearm. With the butt plate against your bicep. Then pull the knob with your fingers. This gives you excellent bracing and a positive grip on the knob. But in the end, no one will ever accuse the Mosin safety as being as easy to use as a Remington M700.
Now if you want to talk about lack of safeties on issue rifles, the French had a real aversion to them.
dalee