The Megaminx is simply put, an expansion of a 3x3x3 in terms of its solving, it is not too difficult to learn if you know how to solve a 3x3x3 but takes much longer. Speedcubers will initially solve a star similarly to the cross but with an extra edge, then F2L can be done, this process is then repeated for a few more sides until they get to the last layer. There are lots of excellent megaminxes available.