I previously used EmpowerGMAT for one month to study for the GMAT.
EmpowerGMAT had great video explanations for practice questions and presented some unconventional ways of solving problems. There were different study guides (1-month, 2-month, etc.) depending on the pace you wanted to go every day. What I found particularly helpful were nailing down some common difficult math questions. If you are debating whether or not to use EmpowerGMAT, I would say go for it! You can always start off with one month and purchase more months as needed.