Welcome to ECF, Graeme Tolley.
The products I use all the time have remained stable, with occasional upgrades in features or power. Like many, I started with Ego-T batteries and plastic clearomizers. That was in 2012, and those are still around. Soon the higher power Ego came out, then the glass tanks, then the "twist" batteries and spinners with even more power. In 2014 or 15, I started seeing lots of positive reviews of the eLeaf batteries. I was giving away Egos to smokers who wanted to try vaping, so I switched to the eLeaf 30W. Three of those in rotation kept me supplied for five years. During ban panics I bought more eLeaf 30W and the later 40W for storage, as well as bunches of BVC glassomizers and coils. The glassomizers last forever and travel well, even the seals being slow to wear out.
I feel very secure with these choices, but I sympathize with those who are in the discovery phase of vaping and are not yet sure what their "forever" setup is. Vaping becomes cheaper when you do have your "forevers". I'm curious as to how so many new things are coming out when there is the pmta process required.