I took femara/letrozole for three months. I got great results every month...two really nice sized follicles. However, I did not get pregnant. I also took clomid for one month and the side effects were horrible. I produced 8 or 9 good sized follicles and felt like crap. We had to sit out that month because of the risk of multiples. The good thing about letrozole is that it only helps you produce one or two really nice follicles. Also sometimes letrozole works when clomid doesn't. It is also out of your system faster than clomid. Within 2 days of taking your last pill, your side effects go away. The only real side effects I had were headaches and mild hot flashes.
Letrozole is used in breast cancer patients but REs here in the US have started using it for fertility. It is not marketed for fertility but after some research, I decided that I felt much safer taking letrozole over clomid.