This is difficult to advice to another person since it is all down to preferences.
The SD is a great device and the only thing it lacks compared to a Tornado battery is constant voltage.
The output voltage will vary during the "load cycle" of the battery, it will drop and become lower the lower the charge is.
On The Tornado you will get constant voltage of 3.3 volts during the whole charge. (Almost)
One great advantage of the SD over the tornado is that if the SD broke you can get spares and repair it.
If a Tornado battery break you have to bin it.
In A SD the battery cells are replaceable.
One advantage of the Tornado battery is it size, it is very small and holding it is very comfortable.
Although the SD is not big it is much bigger than a Tornado Battery.
Hope I have helped you more than confused you
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