Well I have both, so here goes.
I ran with folded steel glasses for a while. After using my samurai helm, i upgraded to the folded steel because they are basically samurai helms with 8 strength bonus, so 1 mod better.
They worked fine, but then I upgraded my templated to the basic samurai vamp form template everyone uses.
Mace and shield glasses are excellent. With a crimson/jackals your dexxer will hit their 150 cap. +10 strength doesn't hurt either, plus hit lower defense works on everything. Great glasses.
Now, I can see only a few reasons to switch to folded steel.
1) You have dexterity of +5 or more in another item to reach your 150 cap. Combined with a weapon that has hit lower defense already, you might not benefit as much.
2) You do group hunts alot. Chances are if you have a guild that does peerless and or doom hunts alot you might not benefit from your hit lower defence, because chances are someone else will have the monsters in "lowered defense". Thus that property might not do anything.
In my opinion, I havent' looked back after getting my Mace and Shield glasses. They are excellent. Sure the folded steel is nice also, but unless you meet a very slim type of character/armor layout, the mace and shield will benefit you more.