I'm guessing that app allow you to discover LTE cell towers and it found a few. For me, a signal strength of -85dBm can be considered 4-5 bars and very good. Above -100dBm is acceptable, but won't get you the best throughput. -105dBm or lower tends to be 1 to 2 bars and not very good speed and lower than that is when your signal will began to cut out.
3GPP release | User equipment category | Maximum L1 datarate downlink | Maximum number of DL MIMO layers | Maximum L1 datarate uplink |
---|---|---|---|---|
Release 8 | Category 1 | 10.3 Mbit/s | 1 | 5.2 Mbit/s |
Release 8 | Category 2 | 51.0 Mbit/s | 2 | 25.5 Mbit/s |
Release 8 | Category 3 | 102.0 Mbit/s | 2 | 51.0 Mbit/s |
Release 8 | Category 4 | 150.8 Mbit/s | 2 | 51.0 Mbit/s |
Release 8 | Category 5 | 299.6 Mbit/s | 4 | 75.4 Mbit/s |
Release 10 | Category 6 | 301.5 Mbit/s | 2 or 4 | 51.0 Mbit/s |
Release 10 | Category 7 | 301.5 Mbit/s | 2 or 4 | 102.0 Mbit/s |
Release 10 | Category 8 | 2,998.6 Mbit/s | 8 | 1,497.8 Mbit/s |
Release 11 | Category 9 | 452.2 Mbit/s | 2 or 4 | 51.0 Mbit/s |
Release 11 | Category 10 | 452.2 Mbit/s | 2 or 4 | 102.0 Mbit/s |