They are clearly very different circuits. The MMD operates at 24 volts and uses newer BBDs that are easier to source. The TT operates at 9 volts and uses the original, rarer, and usually more desirable Panasonic BBDs. They clearly sound different, and most people prefer the sound of the Panasonics in the TTs.

But there are a couple of things you give up going with the TT. First, the MMD has a dry out so that you can send the dry signal and the delayed signal to different amps or channels on a mixer for delayed stereo separation. The TT has a loop output which is cool, but no dry out. Also, the TT seems to be noisier and more glitchy as you add delay. Even within its standard delay range of 550ms, you get more noise and lower fidelity as you increase delay time. When you go beyond 555ms using the tap tempo, the delays get really low fi and even start to go into ring modulation territory. Of course, you might like this. The MMD can’t go beyond its max delay time because it has no multiplier circuit, but it stays clean, at least as clean as an analog delay can stay, through its entire range.

It also seems like it’s easier to overdrive the front end of the TT. The MMD has a LEVEL control and the TT has a GAIN control that both allow you to adjust the level of the signal coming in. They also both show you when it’s clipping. It seems like the MMD has more headroom than the TT. It might be because of the newer chips. It might be because it operates at 24 volts. It might be both.

I’ve never had a chance to try them both next to each other, but I wouldn’t be surprised if after A/B-ing them, some people think the MMD “feels” better, or works better for them even though the TT has more bells and whistles.

If you do go with the MMD, don’t forget to brightly mark the 24V plug because it might fry your 9V devices if you accidently plug it into them.