You can cancel immediately and still get that initial trial/month! I always do this, especially for apps i aspirationally purchase a subscription for a year for (fitness/language apps).

Yeah as a rule I cancel every service immediately after payment. If I still need it in the second month I'll just buy another month, it takes seconds and I don't need to track anything. (Only exception being a music subscription, the only thing I use on a daily permanent basis.)

I would much prefer if all services offered an option to buy only one period rather than always requiring manual deactivation - but I also understand they make a lot of money from people paying for things they aren't using.

I do the same. Then when I lose access and I actually care, I know that's something I should support.