It works pretty well. We use it with two identical Samsung tablets, one as the prompter, one as the controller. We load the text into the controller tablet, which slaves (and reverses) to the prompter tablet which slides into the prompter housing I built (I need to do a little how-to video on this which I have promised for a long time, it's a full-blown prompter that can be set up in less than four seconds... literally).
The developer is a friendly guy (somewhere in Europe, don't remember exactly where... Denmark, maybe), who will promptly answer emails and readily takes suggestions for improvements and features.
The app is free... EXCEPT... you have to purchase an app upgrade if you want to use two tablets and slave them together like we do (via Bluetooth), and you have to purchase the upgrade for BOTH devices. But... it's something like $1.95, if I recall. But if for some reason you do a force stop or clear the cache or uninstall and re-install, then you have to purchase it again. We've done that a couple of times... but again, it's only like two bucks.
I'd say it works pretty darn perfectly, EXCEPT that I wish the speed control was a little easier and more intuitive. I need to make some suggestions to the guy about that, but haven't. Also, if you don't know what you are doing it's easy for the speeds of your devices to get out of sync (the key is to NEVER change or even TOUCH the speed control on the "prompter" device, always just launch it and leave it as default, ONLY change speeds on the "controller" device... and then you'll always be in sync).
You can also, say, use a tablet as the prompter and your Android phone as the controller (we've done this), but to make sure both are in sync you really are best having two identical screen sizes (even better if you have identical devices like we do... the tablets we have for prompting are identical, except we bought one black one and one white one so we could easily tell which is which, we always use the white one as the controller).
Fantastic Plastic Entertainment, Inc. fantasticplastic.com