We were deciding between the blue bluebird and Ampex 436. psychologically I could not get past the hundreds dollar difference and I assumed the blue bottle was worth the increase in price. My assumption was not accurate. Both mics sound great, however, the blue bottle sounds like a lot of mics I have heard before, while the blue bird has a unique tone of its own. The blue bottle is a much "hotter" mic and it tends to break up a lot easier, it kind of has a tube thing going on. Ampex 436 is a lot more natural and has a true to life sound, in other words its not trying to be anything, it just is, and that is where it works beautifully. I will mention this mic is extremely tight sounding and has low noise, you will be impressed. The 436 has a lot more clarity and detail than the blue bottle, while the blue bottle has more full and bassy tone. The bluebird is an amazing mic for the money. One thing to remember don't ever use any mic without a channel strip, your quality will go up ten fold.
Buy this mic if you are on a budget I tried a ton and this mic sounds like some higher end mics, no joke. I am not sure how they made this mic with a $$$ price tag, it is very impressive. Don't waste time, just use this one over the blue bird or the baby blue bird. The people at guitar center wanted me to get the Blue Bird, but the Ampex 436 just worked better for us and with our acoustically treated space it sounds amazing especially when recording live drums and guitars. It really give the kick drum a nice thump without having the stomp the kick pedal down really hard.