"1) Is Waterbabies worth it in your opinion and until when did you continue? I am worried that DD might not like a normal pool with colder water."
I've been babyswimming with my daughter from 3,5 months old and she never stopped attending classes until she was 7 - not babyswimming then anymore, of course ;) With my son I started at 7 months. He's almost 2 now and we still go.
I wouldn't need any classes with my son, because I became a swimming instructor myself when my daughter was 2,5 years old - 12 years ago - and worked as one for quite a while. I just think the group setting is nice. We also go to the pool apart from the lessons - usually we simply stay longer afterwards.
As for the pool with colder water: When they are small, the stabdard pools are simply too cold for them. Once they are older they are as fine in a colder pool as they would be without being used to a warmer pool - so it completely depends on the child. Just like being used to warm water in bath doesn't make them not like colder pools.
"2) Is dunking the babies under the water useful for learning to swim later on?"
Yes! You can't swim properly, if you aren't comfortable putting your head under water! It's also a safety issue. A child can't be safe in or near the water, if it's not used to being under water.
"2) Did you do the photoshoot, and what are your thoughts on this?" I wouldn't do a photo shoot I had to pay for. When my daughter was small, the teacher and sometimes other parents would occasionally bring simple underwater cameras with them, make pictures during the class and send them to us. In my son's classes, a preofessional photographer visits the class once or twice a term and makes photos during the normal class and everyone has the chance to make underwater photos as well. The parents pay the individual photos, if they want to have any. But also here some parents (me for instance) would just occasionally take private cameras with them and make photos. Of course it's not the same quality, but seriously, who cares?