I used to use a BT4.0 dongle with my Duo to connect to my iPad without any issues. Although, It was a bit slower than connecting to a computer via a USB cable, it was still very usable.
Last night, I took my new Dwarf for the first time to the rehersal studio with the band and used that BT4.0 dongle in the Dwarf to connect my iPad.
The connection speed was excrutiating slow. It took literally 5 minutes just to draw the pedalboard on the browser (Safari on the iPad). Accessing the pedalboard list, it never finished redrawing the pedalboards thumbnails.
The iPad was only 1 meter (3 feet) from the dongle (Dwarf on the floor, iPad on the table).
I admit that the dongle was connected to a USB hub into the Dwarf. I use a hub because I also need to have a MIDI keyboard controller connected to the Dwarf.
So, I will perform more tests this weekend but, at first glance, it seems that the Dwarf does not handle Bluetooth the same as the Duo does.