That's a pretty big let down right there. Tapatalk is the de facto standard on droid devices. Guess which mobile platform has the biggest market share right now. Droid.
Droid, as in Verizon Wireless? "Droid" is a brand name used by Verizon to describe their brand of Google Android-based cell phones. Tapatalk works on devices other than Verizon Wireless branded Android-based devices.
Reasons why TapaTalk is not the best path to choose: You may think that Tapatalk my be a defacto standard, but for an owner who has come to depend on income from his forums; Tapatalk provides no website monetization abilities such as AdSense, VibrantMedia, DoubleClick...etc.
If you have a forum that gets a lot of organic referrals, pushing a third-party app ("This forum has an app for Android/iOS. Click OK to learn more about Tapatalk") in to the user's face before they know anything about your site, makes for an incredibly bad first impression. It ranks right up there with the, "Please take a survey to improve our site" and the, "Hello, my name is AMERICAN-NAME, how can I help you today?" pop-ups that you get at support sites within three seconds of loading their first page.
UBBSystems has the right idea here. Follow current web standards and create a responsive mobile website. One that you will have complete control over it's look, feel, and up-time. It's beyond me as to why anyone would rely on a single unknown third-party developer to build a stable and fully functional app that you have zero control over is release schedule or functionality. If they release a buggy app version and don't fix it for a few days/months, there is nothing you can do except tell your users to wait for a fix... and who knows when that fix will arrive? On iOS, users cannot roll back to a previous version. On Android, it's not imposable, but not simple for non-techie users. That's like putting your eggs in someone else's basket.
And what about users of FirefoxMobile or WinPhone7/8 or Ubuntu Mobile OS or other small screen OS's? They'll get left out and probably will instead browse your competitor's website because it provides a better user experience for them -- probably one that utilizes a responsive design