Complicated question. Bluetooth 4.0 + LE (a.k.a., Bluetooth Low Energy) almost certainly uses less energy than Bluetooth versions less than 4.0. I don't know how any Bluetooth version compares with any of the many WiFi versions or which WiFi version these cheap dongles use.
iOS has not supported Bluetooth versions earlier than 4.0 + LE unless their use was certified by Apple. I don't know whether this was due to the inherent insecurity of these earlier Bluetooth versions, to their potential high energy usage which could drain the battery of an iOS device, or for some other reason. So if you have an iOS device, the dongle needs to be Bluetooth 4.0 + LE or certified by Apple which these cheap Chinese dongles aren't.
In the wild, anything-goes Android world, any Bluetooth version is likely supported.
So if you will be running BimmerCode on an Android device, the Bluetooth dongle that you ordered will probably work. If you run BimmerCode on an iOS device, your Bluetooth dongle might not work. A WiFi dongle would work with all portable devices.
The methods used by the BMW Connected and iRemote apps and the ConnectedDrive Website to access some i3 data and control some i3 functionality have been reverse-engineered. I am not aware of any effort to reverse-engineer the data packets on the i3's several data busses to be able to do what you, I, and many other i3 owners would like to do. Doing so requires some electronic equipment, smarts, and lots of patience.
Something similar was done by a couple of owners of early Honda Insights who then built and sold custom gauges and control devices. With fewer than 20k Insights sold, the market for such devices was tiny, so the efforts of these talented owners was based more on love and curiosity than on profit. With many more i3's having been sold, there would certainly be more potential customers, but many i3 drivers are temporary lessees who might have little or no interest in such devices.
Insight owners are probably quite different from the typical BMW owner. However, some i3 owners are or were Insight owners, myself included. Many i3 owners like me have never owned or been interested in owning an ICE BMW, so there might be hope for the development of some of these devices. Maybe as the cost of used i3's continues dropping, which encourages long-term purchases by non-traditional BMW owners, as factory warranties expire, and as the desire of these more committed owners to detect and fix problems to minimize the high cost of BMW parts and service increases, someone will develop and sell such devices.
