This is by far the cheapest multiband compressor with sidechain that I could find, and it works great. Very transparent. Everything else out there is over $100. ToneBoosters offers similar products for a fraction of what their competitors charge.
Imma be quick on thisone. This is hands down the best dynamic EQ I've used. Don't get me wrong. I've tried pretty much all the major ones and they are awesome, but I always get lost in that "range" parameter. Fix draws you classic dynamic curve for each EQ filter. This makes it super intuitive to use. It also sounds great. I've been able to save some pretty sh***y recordings with it. Can't believe it costs only 19 Euros. It's an absolute steal.
This is an outstanding product. Just as an EQ it earns its place in any studio - 30 different filter types which all sound just as they should. There are also AutoLink filters where you simply place the points on the frequency graph to 'draw' the filter curve - so you get the best of both worlds. On top of that you can also define a compression curve for each filter to give you dynamic EQ. In fact it's more flexible than just compression - you can draw almost any kind of curve for some really interesting effects. I think some people may overlook this plugin because the flx name doesn't really hint at the dynamic EQ possibilites. The potential really is endless with this little gem and it looks fantastic too. It doesn't sound good or bad - it just sounds 'right' - it does its job without drawing attention to itself - exactly how it should be.
ToneBoosters is a great company - don't be fooled by the low prices - their business model is based on selling the highest quality plugins at very affordable prices. They're also very fair - you can download and try full versions of the plugins before you buy. I own this and the TrackEssentials package which is also great value.
Update 21 Dec 2014 - I've been using this for a while now. The possibilites really are endless, but one very useful thing I've just discovered is how great this works as a de-esser. There are two versions of this plugin (both included in the price) - you need to use the FLX4 plugin that has a sidechain input. I use an EQ to broadly filter out everything except the problem frequencies, then I route that to the sidechain input on TB Flx4 and use it to drive the compressor curves of the filters - then you can fine tune the flx filter (s) to sculpt out the problem frequencies. It's not like multiband de-essing because you can partially overlap the filters, and use different compression curves and attack/release on each one, so it's much more powerful. Most singers have a distinct 'ess' profile, so it's easy and quick to fine tune the filters for each artist.