If you delegate 1000 SP to @minnowhelper, you can expect approximately 0.100 SBD|STEEM per round. This value may vary depending on how many bids the Bot recives.
The other Bots are not yet popular. So it's too early to give a profit forecast.

With 10 rounds per day that could be 1 SBD/steem per day is 7 per week. Which results in 0.7% return on investment on weekly basis.
If my calculation is correct, that is much higher than on the normal stock market or my savings account

your calculations are correct, you can see the payments of 3 Investors who delegated about 1000 SP to @minnowhelper. (thorheit, mynaturebody and truconspiracy)