According to the specs:
4.8in x 2.6in on our triumph
4.5in x 2.3in for the iPhone
The keyboard you mention will look great on the triumph, as our phone is flat I would like to try this myself. There are more keyboards so looking for the best one takes a lil more effort in research, especially if the keyboard offers a built-in battery and sexy looking.
If I could mod it, I would remove the stubs that originality hold the iPhone and make the base flat, make a cut on the left where the camera would lay itself at, then I would get some double sided tape and place them at the battery door or on top of the cases by the sides (preferably on the sides of the battery door without case)(I recommend you get a TPU or hard case if you still wanna keep your phone clean). We can continue the conversation, I'll go look at more keyboards.