Does anyone know if SSMS boost still an active product?

The last release was over a year ago, a lot of this forum seems to be pretty dormant and a support email sent weeks ago has not been answered.

I am thinking the same that all looks very quiet and am considering purchasing a license.

Just so you know there are a couple of features that have stopped working in the recent versions of SSMS (I'm currently using 18.12.1), and SSMS Boost haven't even acknowledged my emails or tickets about them, sent many months ago. I expect SSMS 19 will be released in a month or so (it's currently on Preview 3) and I'm anticipating more broken functionality in that.

If you haven't already done so it might be worth putting the trial through it's paces to make sure the features you're hoping to use actually work.