Thank you for your comment @rezoanulvibes, I wrote an article about that:
https://steemit.com/steemit/@gmichelbkk/is-it-still-profitable-to-bid-for-steem-upvote-bots
Using bots is not always profitable because you may get less SBD than what you paid, but you always get much more SP and altogether the revenue per post is always more. Using bots, the post get more exposure, more new followers, and people commenting and upvoting like you get more rewards.