Before you switch due to constipation, you should give Colic Calm a try. It helps with the baby's little digestive system and helps with constipation. You can also try making some Chamomile tea and mixing the formula in the tea. The tea soothes their stomach and also helps with their stools.
Although my son suffered from constipation and know EXACTLLY how you feel, I wouldn't quite give up on this formula yet before you try other things to eliviate the constipation. Dairy Formula sometimes tends to constipate babies due to the baby not being able to break down the protein in the milk, however, if you try some other remedies, I am sure you can get the constipation under control and still be able to offer your baby the BEST formula on the market right now.
Trust me, I've tried Similac, Similac Sensitive and Similac Alimentum...all still made him very colicy, gassy, reflux, sleepless nights etc etc...