The efficiency isn't a huge improvement over the X10:

X10 @ 630W for X11 algo or 63W/GH
G28 @ 1300W for X11 algo or 46W/GH

The other algos seems to have a similar efficiency increase. Not insignificant, but not a game changer either. To give an idea what's possible efficiency wise for X11:

Spondoolies SPx36 @ 4400W for 540GH is 8.1 W/GH
Innosilicon A5+ @ 1500W for 65GH is 23W/GH

The one advantage here is there are multiple algorithms available, so Bitmain can't nuke the algo and make the miner worthless.