One of my friends had gastric bypass surgery and he was once in absolute agony because he was tempted to try to eat a little more than the tiny portion he was supposed to have... The weight loss only comes with eating tiny portions.
The problems are that you have a bigger struggle to get the nutrients into that - and of course you have to continue with the tiny portions every day for the rest of your life... You can never have a day off - no matter how special the occasion.
I personally found that by exercising and choosing carefully which foods I ate I could lose weight without the pain and dangers of surgery and for me - surgery would have been more effort. Having said that - I have never been good with tiny portions... The idea of being stuck on them for the rest of my life would be very tough.