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Actually not a lot, all these tools parse your HTML and preview you with the page that they load it with. The difference in using the tools is that they'll check the page with a different user agent. So if you do any check on this on your current page it will tell you how the page looks like.

Thanks for the responses. I'll be analyzing the traffic that we get from the different devices.                                                The site is not responsive design; because of the size and nature of the content, we had to go for adaptive design. Right now we have javascript that detects the user agents and deliver the appropriate CSS formatting.                                    I am wondering if Phablets (specially iphone 6plus) will behave more like tablets, or like a smartphones.