I use the Libre CGM system, coupled with a MIAOMIAO add-on & GLIMP software on my cell phone. The Libre itself is not very accurate. However the GLIMP software on my Android phone ahs an option to send BGs to another person/phone. I do not need or use this feature. GLIMP software also let you enter finger-stick BG reading. That makes it far more accurate.
The GLIMP software also has an ALARM function, you can set, (both high & low BGs. For people that hate finger sticks, morning noon & night, tis GREAT. When I start a new sensor, I do a finger stick at a relative low end, not hypo, a med BG reading, and a high. Then the GLIMP starts giving CORRECTED results, and also in smaller text raw sensor readings. All this sounds more complicated than it is in reality.
Before I got the MiaoMiao, I tried a BluCon, I was NOT happy with it. Too many problems with it. The MiaoMiao is a little more expensive but it was worth the extra cost. The MiaoMiao was about $125 usd.
I ave heard of he Dexcom, I think it's a bit expensive for me. I had a serious need for a CGM, I became BRITTLE, swinging both highand low quickly, on a limited budget. I think the Dexcom is a lot fancier unit.