I recently replaced my aging flint/magnesium blocks. After carrying them and using them for many years they were in bad shape. I looked on ebay and found the flint rods, about 1/4 thick by about 4 inches long. Five for about $15.00. I also found someone selling magnesium shavings, a gallon ziplock full for about $10.00.
I now carry my flint rod and two match cases tied together. One match case has cotton balls/pj and the other has the shavings.
I have found that they light easy and a small pile of the shavings not only burns with a flame for several minutes but it leaves a red hot ember for about five minutes. The 4000 degree flame will light almost anything even if it is cold and wet outside.
I always carry a lighter, stick matches and lifeboat matches as well. Although the flint is my backup I find myself lighting my fires with it just for the practice.

The problem with preshaved magnesium is that as it oxidizes, it gets harder to light. On a mag block, it is pretty much confined to the surface, like in aluminum, but when you have shavings, you mostly only have surface.

I never thought about that. I will have to leave some outside for a while and test it again after it oxidizes.

If space is available carry the Mag/Flint, better to have it and not need it than be in a situation of needing it and not having it.
When it comes to something as important as Fire, always have back ups to include PJ cotton balls, Fatwood etc.

Actually, I like the weak bond between the flint bar and the mag bar. I just pry out the flint bar, fashion a epoxy handle for one end and when the epoxy has dried and set, drill a lanyard hole and viola! your own firesteel for half the cost.....

I too don't care very much about the magnesium....

I have never considered the mag bar 'bulky'

Easy firestarting is PJCB and a spark from something...sparklite, mag bar flint, firesteel, hot spark...whatever

The mag is a good little extra umpfffh for less than optimal natural tinder or I want to practice.

A mag bar and a 35mm film can of PJCB is a great minimal fire kit.

Is it better to make some magnesium shavings before hand and keep them in a water proof container? or it is dangerous to have the magnesium shavings stored?

see this post, same thread

From personal experience:
Tinder-Quick tabs make a critical differance. Irrespective of which firesteel or magnesium block you use. They either take a spark directly or can be used to catch magnesium shaving. If you need to boost the initial thermal impulse.

Maya wood or fatwood is second stage tinder. It's excellent as a booster (as shavings),but I would not be happy relying on it in a shivering wet This Fire Light's The First Time Or I Am Dead situation.

If you have Tinder-Quick, you don't need magnesium.