I have used GMAT Club Tests. I find these tests really useful. Not only i get to increase my quant solving speed but these tests are useful in learning quant tricks and strategy too. It is more efficient to learn from questions than from quant strategy books. GMAT CLUB Tests boosted my confidence. I have been studying GMAT from almost a year, i read almost every book but i was not able to apply strategy during tests. I used to get panic and chickened out from exam. I discussed my issue with my friends who had already appeared for GMAT and scored high in GMAT. They suggested me to use GMAT Club Tests. GCT really helped me. I would recommend GCT to every person who is appearing for GMAT and want to boost quant score. I haven't used GCT Verbal test much as i didn't need it.