From a previous post:
"Yes, briefly... they both went black for a few minutes... never found out why.  The two EFIS are linked.  I guess it could happen again.  If all electrical went, the Garmin still has a couple of hours on its internal battery, with its PFD."

One of the great things about building your own airplane is you can put whatever equipment you choose in it.  With that freedom comes responsibility, and risks.  When considering options for your equipment also think through all the potential problem situations you can, then talk to other pilots, especially ones with lots of experience, and read accident reports.  What can go wrong with your panel in flight?  Well, lots of things.  I've built some panels and flown with several pilots, helping them check out their panels, and seen surprising things.  Most problems were seen in the first 50 hours or so, which you'd expect.  I've seen EFIS displays do strange things, even the more expensive ones.  One example was a system with synthetic vision that flipped upside-down just before the landing flare. Rather disconcerting to suddenly see the runway at the top of the screen and the sky at the bottom.  It only did it at certain airports.  I've seen an EFIS slowly tumble while in straight and level flight.  It had to be power cycled to bring it back. I've seen dual EFIS disagree with each other, even when linked together.  On another dual EFIS setup one or both displays would randomly reboot.  This was a high end system and was supposed to be fairly mature.  Turns out the specific combination of equipment and interconnnects used on this plane, while perfectly valid, had not been thoroughly tested by the manufacturer.  They fixed it, but it required multiple software updates to get it right.

Speaking of software updates, that's something else to beware of.  Even well tested panels that have been operating trouble free for hundreds of hours can suddenly develop a problem after an update.  It's not uncommon for an update to fix one problem but create another one.  Never launch into IFR conditions right after loading an update.

Now I'm definitely not saying you shouldn't go with a glass panel; they're great.  I love 'em.  Just be aware that losing electrical power isn't the only thing you should be concerned about.  Put some serious thought into your backup equipment and make sure it will serve your needs if the glass ever goes dark; for whatever reason.

Tom Gourley