I have tested @buildawhale and a few other bid bots. The percentage you get is based on the amount you bid. I have used an algorithm to calculate profitability, and have gotten 10-65% profitability with different bid bots. These profitabilities depend highly on the individual 2.4 hour bid windows, and it is possible to lose money at no fault of the bot in an overbid bidding window.
I have always had positive responses, support and feedback with @buildawhale.
That said, I suggested that theMarkyMark would suggest BuildaWhale as an answer to your original question, since it is his baby.
And the other 4 out of 5 would be?