There's no sticky sessions, and the balancing is purely random (so statistically roughly the same as a round-robin) - it was primarily designed for large numbers of small backends, rather than one or two sites with ten backends, though we'll be adding in more balancing types as we go.
By purely random, you mean not weighted, so all your backends need to be roughly equal in capabilities?
Exactly, as at Epio all our backends are identically sized. Obviously this isn't the case for everyone - but it's easy to add that code.