Both bluetooth and OTG work fine. I did notice that not all cables work though. I'm using the charging cable that came with the tello. I'm also using the Mi2 WIFI extender for the tello.
I use the same cable for the OTG between my phone and Spark controller.
So, last week I ordered a DJI refurbished Spark fly more combo. Wow this drone is awesome for the price.
I still love the Tello but the Spark takes some very nice video and photos. Sports mode is a blast at 54kph.