It should have only pop up once unless you have cookies disabled. I have permanently disabled the popup now, which I had done before.
The forum has suppored Tapatalk for years now. I updated the version today, which is causing the popup.
And, yes, you can access the forum without it, but there are members who use it because of it's additional features and ease of use on a small screen. If I'm not mistaken, the latest version adds uploading images from iPod/iPhone/iPad, but I'm not 100% sure.
Shane