*Both CD drives read data at x1, but a stock Duo loads faster than a stock TG-CD because the lens mechanism is more efficient. A CD-ROM with new metal gear replacements is a lot faster than a stock unit, but also MUCH noisier. I haven't compared the speed of a CD-ROM with aftermarket gears to a stock Duo.
*TG-CD has an in-line AC adapter, the Duo has a wall wort.
*The TG-CD uses common RCA cables out the rear. The Duo needs an expensive, finicky, proprietary AV cord wasting space on the side.
*The headphone jack on the TG-CD doesn't function when playing Turbochips.
*The TG-CD needs a system card every time a CD is played.
*The CD-ROM2 can function as a stand-alone music player.
*TG-CD has a dumb TG16 controller port.
*Duo = sleek and small. TG-CD = relic from bygone era more impressive to modern gamers.