I have tried transformers rated at 40-15k Hz that sounded really good.
There was no bass and no highs missing for my ears, even if compared to FLAT rated transformers.
Sometimes, they are talking +-0.5dB 40-15k, but in fact you have a +-1dB 20-20k, and this is a nice response. I think that even +-2dB or +-3dB isn´t that bad, and still usefull, depending on what you are tracking and what you want. Many people uses low or hi cut in almost every track, and if you are missing a little high or low end, you have that marvellous six channel EQ for that... :green:
But any audio transformer can be usefull. I´ve heard people using those 150-10k UTC as mic input and loving it. Probably they ended with a lot better freqeuncy response. Some trannies, like those UTC H series are rated for line levels, so, when you use it with mic levels, the FR is a lot better. You gota try to know.