In my opinion, I think it is kind of similar to bid bots. They are not healthy for this platform but however, we will be able to get something out of it. The most interesting factor about using Minnowbooster or Smartsteem is that, if you sometimes don't have enough time to spend in steemit by reading and upvoting post, you can sell your votes in any of these two platforms to earn you few dollars.

I have set my votes to be sold if it goes beyond 90 %. I always maintain my voting power from 80 to 90 %. There will be few days where I will not be able to spend enough time to read or upvote other posts. During those days, minnowbooser and smartsteem does the job for me and pay me decent returns for the same.