I bought one of the cheap ($15-20) DTMF mics for my Kenwood TK-880. I had programmed my radio for user PL selection, which allows you to change the PL tones from the DTMF pad.
It was a waste of money, because it doesn't work. It seems to work as a microphone, but it doesn't ground the on-hook line through the mic button. That means the scan function is disabled. Not only that, but while the PL select looks like it's working, what it actually does is turn off receive PL globally. I had to remove power from the radio for a moment to get the PL decode to return.
The seller advertised it as suitable for Kenwood commercial radios, including (specifically) the TK-880.
Maybe it can be rewired to work; who knows. And maybe it works perfectly on a Kenwood amateur transceiver. I don't have a TM series radio, so I can't test that. But it certainly doesn't work as delivered on my Kenwood commercial rigs.