pizza stones

Bakers Pride D125 stone deck oven, I have had my ovens since 07, purchased used out of New Jersey. so not sure of manufacture yr at this moment, but I have a few questions about things.

1st: Stones
I had to replace 1 stone recently a yr ago & had a spare, noticing it has fiber like material in it, because of real small fibers on surface. What type of stone is it ??? I did some research on the net & found 2 terms “Fibrament & Cordierite” Seeing that my stone has some type of fiber I would think “Fibrament” so what is really the difference in both. Just recently I had another stone that I have had since 07 with a surface crack finally break through. Looked at prices on the net and “” was selling them for more than $800 a piece. Found another guy in Illinois selling them for $195. So without hesitation it was a no brainer hopped in my car and drove 4 hrs to save $$$$$, get back last nite to the shop unload them (3) & noticed a big difference in look & feel compared to my other stones. Grant it, I completely understand that the new stones I got these guys are manufacturing (pouring) them on site themselves & not selling actual bakers pride stones. 1 side is really smooth & buffed, the underside is a little rough looking which is fine. I get it “you get what you pay for”
BUT I really feel that the stones will be just fine. So what knowledge does anyone have on this.

2nd: To leave oven on or not.
I have been in the business since early 80’s & never really knew any pizza shop leave their stone ovens on 24/7 unless maintenance needed to be done to them. I get the advantage of leaving them on 24/7. What is your opinion on this…