Hey guys, I would suggest waiting for the Turbo Everdrive. It will leave the neoflash version very outdated, and is months away. This will run off of a sd or microsd card so you can put the entire tg16/pce library on it and forget about it. There's talks of integrating the Arcade duo card into the Turbo Everdrive, but I'm not sure he's interested in doing that. He's speccing it out to be more around the pricing of the everdrive md which is $78. So if it's around $100 it's still cheaper than the group buy price for a 128mb + save neoflash cart and better. Grant it, the price and release date is still speculation.
Here is the forum thread where you can track the progress over at assemblergames. Admittedly there isn't a whole lot of progress since he's working on the new everdrive md. http://www.assemblergames.com/forums/showthread.php?t=31764. Retrocollect article on it, the link to the Turbo Everdrive shows the pcb design. http://www.retrocollect.com/News/krikzz-to-release-pc-engine-turbografx-16-flash-cartridge-a-updated-ultimate-mega-drive-everdrive.html
tl;dr Why drop more than $100 for a cart that you will be replacing with a better one for around $100 in around 6 months?
Here is the forum thread where you can track the progress over at assemblergames. Admittedly there isn't a whole lot of progress since he's working on the new everdrive md. http://www.assemblergames.com/forums/showthread.php?t=31764. Retrocollect article on it, the link to the Turbo Everdrive shows the pcb design. http://www.retrocollect.com/News/krikzz-to-release-pc-engine-turbografx-16-flash-cartridge-a-updated-ultimate-mega-drive-everdrive.html
tl;dr Why drop more than $100 for a cart that you will be replacing with a better one for around $100 in around 6 months?