I know this is an odd thing to say, but I've used a c37a more than any other microphone other than a SM57. I had access to a pair for years and used them on everything. When a C37a works on a track, which is most the time, they are just heavenly. Eventually I had to return them and sought out the Tonelux. In regards to the one I got, it was a pretty serious disappointment. The sound was quite mid focused, muffled overall, and it did not respond at all like either c37a I had used before. In a shootout on a track where I'd previously recorded the vox with a c37 the tonelux ended up last in last place, best to worse being the c37a, UM57, Rode nt1a, tonelux. I have to mention it was no contest as well. Distant fourth. Very poor showing.
I am not a professional engineer, I play keyboards for a living and record mostly my own music. I'm sure an audio wizard could have achieved better results than me, but the fact that I enjoyed the sound of the nt1a, a mic I really don't care for honestly, over the tonelux had me returning it as fast as possible. I think something may have been wrong with it, as I later saw the same mic resold at a steep discount.
I'm in the midst of cloning a c37a now, it's not prohibitively expensive to get the parts together to do it. Here's hoping it turns out ok.