In practice, I found the One Touch Verio meters (I used to have another but gave it to my father) to be wildly inaccurate. It was common for me to get two readings as much as 2 mmol/l apart and got to the point where I had to average the three readings together.
Admittedly, I didn't use the One Touch Ultra meters much and only went through about 200 test strips.
The Accu-Chek Aviva Expert was my only meter for the past ~4 months and it was very close to my a1c. Note: I did have an issue with either low batteries and/or bad test strips with this meter. It consistently yielded readings in the 7mmol/l range. I kept giving myself insulin corrections and thought my honeymoon phase was completely over when it didn't do anything. Finally, my Dexcom CGM started to alert me of a low. I tried a different meter and found out my blood sugar was in the 3mmol/l range. Haven't had issues since then though.
I'm not using an Accu-Chek Aviva Connect which I think is called something different in the UK. It's the meter that sends all of your readings to your phone via Bluetooth. No complaints so far.
If anyone has any requests on how I can make this information/resources valuable to them, I'd be happy to do my best to help. Science projects are fun, lol.