Sadly the forum search doesn't work as well as google. I tried mdisc, m-disc, and mdisc and came up with zilch. And there's not a thread in blank media with any tests. I was more interested in burn failure rates and personal experience, but at the current size/price I'd never be able to afford them.
When I first read about them yesterday, for some reason I was thinking they were BDR discs, so $20/5 discs seemed like a bargain. Then I saw they were DVD's. Wow! And shipping on their site is like $13.50 for one set! That comes out to $1.50 / GB, which is nuts. 2TB of M-Disc would cost you $3000! Okay if you bought the 25 packs it'd be $86.58, or $1.29/gb, or $2598/2tb, but still...
I could buy 25 hard drives for that price and have FAR more data security than M-disc because you could have 2 mirror drives at 12 different physical locations. I have a feeling their only clients will be government where waste is the name of the game.
Edit: Just tried adding ~2tb of M-discs to my cart. Shipping is FAR more reasonable in bulk. $18.22 for 18 25-packs, so $1323.22 total. $0.65/gb. A lot better than my previous calc, but that's still ~13 hard drives for the same price, 2x @ 6 locations, etc. The ONLY benefit I can think of is, if their claims are accurate, you wouldn't have to do any maintenance on the discs like you would with HD's (spin them up every few months to prevent lubricant from drying on the spindles). It's too bad though. I was excited to see someone was trying to address the longevity problem. A BDRXL M-disc would be awesome, but it'd probably cost $300 / disc.