Overall SpoofApp works as advertised, it's a simple application that can easily morph a user's voice, mask a caller ID phone number with a number of the user's choosing, and record calls with simple touch-screen option choices.
When having fun with friends, SpoofApp is a great prank calling option. Unfortunately it's also a great way for less than humorous users to harass people who may not normally pick up the phone for them -- I guess I found the bad in the fun, but it's a valid point.
Overall it works as advertised, costs quite a bit to use thanks to by-the-hour billing, but uses a refreshingly simple user interface. If you have $10 an hour to spend I say go for it; at least try out the free five minutes, you won't be disappointed.
Although the app is subject to misuse, it's really intended as just a fun app, so you might well question the overall cost just for a practical joke -- there are plenty of free and strange Android apps out there after all. If the cost irks you remember that your calls are recorded and saved on their secure servers, so you're paying for more than just the time used, you're paying to access the SpoofCard servers and store your personally recorded calls. One bonus it has over other apps too, is that your location in the world is no barrier to using this app, it just uses different numbers depending on your location.
With secure servers, fun features, and a simple interface I say give it a try and have some fun with friends. Just remember that with great spoofing power comes great responsibility, so use it wisely!