I certainly agree, from an industry point of view, that the keratin complex is the way to go for any type of straightening treatment before the big day.
In regards to hair extensions, I agree that clip ins are the best way to go. I find that any of the above mentioned (glue, tape, sew) can damage your hair while the clip ins are versatile, especially if your looking for a certain look for the big day but dont necessarily want a permanent look.
Sally's are okay but I do find the quality lacking and the look is not as organic as the better brands.
My personal favorite are bellami extensions. http://www.bellamihair.com/
I have worked with a few different types and I am always pleased with the results. They are a bit pricier but hold up to heat and look SO GOOD!
I have purchased a set myself... I will try and attach a photo