I have great news for you if you missed out on the Firebird group buy here at KVR. Firebird is easily worth the full asking price ($69 at the time of this review).
I casually monitor group buys here at KVR and had decided against getting Firebird based on 1) the fact that I own a couple of other synths that I thought filled a similar space in my toolbox, and 2) comments from users (and a review in CM) that say it is ideally suited for trance, a genre that is far afield from my own purposes.
I can't remember what prompted me to try the demo, but that was what changed my mind, and fast!
The first thing I noticed was the sound. Since sound is subjective, I will just say that I liked it right away. When I listen to a synth I always try to envision whether I can use it in my own music, and with Firebird I was able to hear it almost instantly. I am not a trance expert, so for all I know it *may* be ideally suited for trance, but I was able to imagine it playing a role in my pop/rock/acoustic/ambient recordings.
The other things that really made a difference for me were the arpeggiator (which has a built-in gate) and the drop-down programming menus. The same way that some people prefer to use a roland-stlye "XOX" pattern sequencer, I wish ALL my synths had drop down programming menus. I'm a preset tweaker by nature, but Firebird makes me want to program my own sounds (and I have been doing just that). The "Random" button will give you a whole new leaping off point, including which waveforms are used in the patch. A couple of my "Random" patches were so good I just saved them the way they were without any tweaking at all.
User Interface: the interface is uncluttered, and designed to keep things simple. It does this well. A few users on the forum (myself included) have commented on the appearance of the gui (chiefly the knobs) and Markus has responded with openness and interest. If you break down the gui into its functionality and its appearance, I would give it perfect marks for functionality and say that I wouldn't mind if it got a little bit of a facelift.
Sound: I like it. Try the demo.
Features: If other devs are smart, they will adopt Markus' best features on their own synths. Menus, arpeggiator, random button. In addition, I like that rather than having fully-programmable FX, he has multiple types of the same effect and you can tweak 2 parameters of each. Not revolutionary, I know, but this idea is in keeping with the user-friendly concept of Firebird.
Documentation: Haven't needed it much, but I did glance over it to find out what the "Pop" button does.
Presets: It comes with 300, and they do a good job of showing what Firebird can do. Since it is so easy to program, I would love to see Markus host a preset exchange.
Customer Support: While I haven't had any issues that needed resolving, I gave a ten here because of three things: First, Markus' presence here at KVR. Second, he once sent me an email just to check if his messages to me were arriving marked as SPAM. Talk about attention to detail! Third, like I said, I haven't had any issues that needed resolving, and that is a good thing! I emailed Markus with a couple of feature requests, and he responded very quickly.
Value For Money: It's great. Sign me up for any expansions!
Stability: No problemns there.
I told Markus I would like to see a mute button for each of the oscillators. I would also like to see some more pattern options for the arpeggiator/gate. I would also like to have lots more sounds (which I understand is in the works). I would like to have several skin options. These things are minor and Markus has said that the version 1.1 update will be out soon.