Hi there,
To be honest I would kept it as a strategic guideline for your progress. Like to think about new techniques and devices as milestones. For me it took me 1 year to get a Bathmate, 6 months later I got my ADS. Just last month I started using an air pump.
I haven’t been so consistent through years(started on 2020), for every 4-5 months of training I get 1-2 months of almost zero PE. Still I got gains, almost 2 cms in length and 1 cm in girth. So during this time I would say that, more than about having to switch stuff every 6 months, you need make and assessment and to look for increases of intensity in terms of TIME, FORCE or TECHNIQUES (I would try to go in that exact order).
So for your routines sake, I would put some parameters of time and force. Just as you would do in a GYM, not just the exercise itself but also repetitions and sets.
Good luck