I have had a few over the years. I find them to be exactly what they were meant to be .. a tough, simply built and rather accurate rifle. At the prices they sell for today, its hard not to own one. Essentially, near .30-06 power for under a $100.
The safety is hard to employ quickly, but becomes easier as you become more familiar with it. The rifle can usually be easily field stripped (which I recommend doing before firing. Cosmo will be everywhere, especially inside the bolt). Sometimes the forend bands can be difficult to remove.
Ammo is inexpensive if you choose to use military, which can be corrosive. Special cleaning care is necessary when using corrosive ammo. Commercial ammo is available from Winchester, Olympic, Prvi Partisan and others. I've had real good luck finding the Olympic at gun shows for about $9.00 per box.
The Mosins can become addicting. If it turns out you like it, it will only be a short time before you add a M-38 or M-44. The carbines are neat. They tend to have a good bit of muzzle flash, but are fun to shoot. The M-44's are available everywhere and have the bayonet attached to the barrel. The M-38's are getting scarce and do not have an attached bayonet. They are around, but not everywhere. There are other variations, such as the Sniper models, 91/59, Finnish versions, etc. You will find a good bit of info over at Surplus Rifle.com. Check the Mosin forum.
Good luck and enjoy.
P.S. Take a look at the movie; "Enemy at the Gate". Lots of Mosins in use there.