I got a couple of those Magnavox digital adapters at Walmarts with one of those 'credit cards' which made them $10.
I didn't get around to trying them until this weekend, after hearing of someone who couldn't make theirs work.

My system is typical rural: a rotatable boom antenna into an antenna amp, all carried on coax all the way to tuner card input connectors.
Using today's analog, I can usually get a viewable signal even from WGN in Chicago, 100 miles away.

Both my SDTV adapter boxes are Funai made TB100MW9 badged as Magnavox units.

Unit 1 at first show no output signal, then scanned and found only one channel, then failed to output anything.
Unit 2 failed to even turn on.

Combined with the neighbors unit, that's 3 out of 3 duds.

These units are difficult to set up, as they contain no RF unit or internal display other than an ON/STANDBY light.

Rec: don't wait until Feb to try yours out!