I just got a gateway. Now, I downloaded the latest firmware (2.0b2) on the micro SD card (8GB ) ,and created a folder (games) for a test NDS game. well, I press the start button but only get a white screen . My 3DS XL is on firmware V4.5. I understand I cannot play 3DS games on this firmware yet. But I'm hoping to at least play ds games using the blue card. my gateway is this one http://www.usar4.com/gateway-3ds-gateway-3ds-flashcart-play-3ds-games-on-3ds-xl-3ds-p-8
Gateway 3ds can work on 3ds v4.5,but far as i knew, use 2.0b2 has some dangerous.so if all you want is playing nds games or homebrew,suggested you buy r4i gold,like this one : http://www.modchipfactory.com/wood-r4i-gold-3ds-flash-cart-for-3ds-xl-3ds-dsi-and-ds-lite-p-1.html.
here is the gateway 3ds caed http://www.dsflashcart.com/gateway-3ds-flashcart-play-3ds-games-on-3ds-xl-and-3ds-console-p-284.html here is the gateway 3ds step by step user guide http://www.flashcartreview.com/how-to-set-up-gateway-3ds-flashcart-to-play-3ds-games/