I was an early adopter for sure. This was back in 2016ish when I installed all of the devices. All of the devices were Z-Wave+ (specifically bought for that) but many of them did not support the newer encryption, and it ended up being a mixed network of devices for sure. Only the last few devices I bought supported the new encryption standard that was being rolled out at the time. I ended up getting a new Z-Wave hub that supported it to be able to securely enroll my new devices... but all it did was destabilize the network further.

It just left a horrible taste in my mouth, and once bitten, twice shy is definitely the case here.

The other thing that made things slow was sleepy devices that would wake up to report status. Things like motion sensors that also reported humidity, light levels, temperature and more (I do wish I could find a sensor like that for Zigbee/Thread... the multiple things in one was kinda nice). Every time they would wake up to report it would flood the network with traffic. And with each additional sensor I would have to tweak how often that would happen (and thus how accurate the data was over time) to reduce the amount of chatter on the network.