B-tool requires a reliable OBD adapter like Carista (see https://caristaapp.com/adapter). Cheap adapters may not work or functionality may be limited.
K+D-Can USB cable
INPA-compatible cable is the most reliable and recommended adapter. You will also need USB-OTG adapter to connect the cable to your phone.
Bluetooth connection is slower than USB. Only genuine ELM327 or PIC18-based adapters will work. Bluetooth adapters work well with cars above 2007. In older cars app functionality may be limited or app may not work at all.
ELM WiFi connection is also slower than USB and app functionality is limited in cars up to 2007. Some phones requires disabling mobile data transmission in order to use WiFi adapter.