@Wurst I have no experience with Libre 2 as it is not available in the UK.
However, I use the "original" Libre.
My first impression of it was similar to yours but over time, I have learnt how to make the most out of it:
- it is less accurate at high and low readings so anything under 4 or over 9, I will check with a finger prick
- at night, there is a risk of compression lows: when pressure is applied to the sensor, such as when you lie on it, it will report low
- it is very inaccurate for the first 24 to 48 hours as our body get used to having an alien object inserted into it. Therefore, I attach my sensor the night before I intend to activate it.
- Libre is about 15 minutes behind finger prick. This can be significant if BG is rising fast (e.g. soon after eating) or falling fast (e.g. when exercising). Therefore, I do not use the Libre readings at these times.
- the Libre is "factory calibrated". My body is not the same as "factory man". Some freeware apps such as Glimp on the Android, use a different algorithm to convert interstitial fluid values (what the Libre reads) into BG values which takes into consideration BG readings.
- Libre is not a replacement for finger pricking - it complements it with trend graphs. The value from the Libre is understanding the impact of different foods, exercise, stress, ... on my BG and making insulin dosing adjustments accordingly.
None of the above is helpful if you want to use the alerts. However, I have tried DexCom and found the alerts on that were pretty useless due to the inaccuracy. So what you are experiencing is probably a limitation of readings via interstitial fluids rather than the Libre itself.
As I said at the start, I initially thought the Libre was a waste of money becuase I spent my time comparing the values with finger pricks and deciding it was too far out but now I understand how to use it, I find it an invaluable piece of tech.