It isn't the lowest out there, their 0.5% house edge is not really 0.5% as there are terms before you get that house edge. The 999dice though has 0.1% house edge all through out, there others that has lower than 0.5% house edge, I even heard of a 0% house edge, not sure which one though.
i don't know about 99dice other then the stories i've heard and what people have told me. 999dice seems to be very sketchy at best. I haven't tried it because of what i've heard. Not willing to risk my money there.
I said that i know of. There could be some lower but thats the lowest house edge i know about at a reputable site.