Just got a chance to look at these really closely. The TDK is really not bad at all for a ~$10 IEM.
Wayne was comparing with the GR07BE, but I think the GR07 has a much flatter bass response right up to 1k.
I also looked at it compared to the MH1C. As our ears already told us, the MH1C is much smoother in the treble and highs, but the overall profile is similar, with heavy bass emphasis and flatter mids and highs. Look at the square wave and impulse response... the MH1C is as good as some of the top-tier stuff, like the SE535!
Recently I've been using my SE215s a lot (been on a lot of airplanes), and I came to think that its profile is also quite similar to the MT-300, with a little less bass boost. Tyll's measurements confirm this. In fact, I was surprised at how similar they measure in almost all the plots. Check them out. Bass response is almost identical, the SE215 has a bit more mids and highs, but they have similar tuning at 5k and 10k. The MT300 does have that suck-out at 3k that a lot of us have picked up on. But look at the other measurements - impedance response, square wave, impulse... they're all very similar! That's a $100 IEM vs a ~$20... But, I have to say the Shures do have $80 worth of isolation awesomeness and some of the best tips out there.
Lately I've been into audio books, the MT300 is awesome for audio books, try this IEM with some audio books! heh, j/k. Audio books always sound like crap...