Be very careful with this "feature".  I can not count the number of sites where they lost my business because it was not done well.  Some of these sites will see "Android" or "iOS" and just assume its a phone.  Then I hit it on my 10.2" tablet, and it looks stupid.  Often, these sites are "auto detecting" and don't just default, so there is no way to ask for the regular site.  When done well, its nice when the site is smart enough to offer a good default and also offer to not filter and deliver the regular HTML page.  Also, make sure that if you do offer mobile, and you have a link to deliver the full page instead, that this option sticks as you move throughout the site.  I have one utility pay site that f's up when I go to it with the tablet, but offers the "pc" page.  Click on it, and it will fix the page you are on... click a link, and you are back to the "mobile" version... click on the "pc" link again, and it takes you back the the main page.  If this was a business I had an option to not do business with (its our local utility and I am stuck with them), I wouldn't.  So as I said, be careful and test, test, test