Using a smartphone/tablet as a mouse topic

I found an app while searching for a way to use my tablet as a bluetooth mouse for my rooted Fire TV. I have a wireless mouse and keyboard I can use on it, but since I don't have a hub yet, I can only use one USB device at a time. If I can get Apps2SD to work with a flash drive, at least to see if it would actually work, I'd want to be able to keep that particular drive plugged in. I also use the Fire TV remote on my Tab 3 8.0 for the keyboard, but there are some screens where a mouse would come in handy. Thanks to anyone who can point me in the direction, in case the one app I found doesn't work out.