Pretty Bad. I've done about 14 runs and haven't got past 5 wins even with updated Silverfish. (Average score = 2-3)
However, oddly, bot plays really good in standard/unranked (WR = 80% with near basic shaman).
Specifically noticed much much slower plays and frequent roping in arena, so wouldn't recommend.
Arena is the better way to expand both gold and card collection (which is the aim of botting), but ranger isn't tuned to do well in that mode, yet.