Other big disadvantages to the UAD-2
1. You cannot sell or transfer individual plugins. You must transfer a card and all of the licences that are attached to that card if you want to sell. This is a long term investment.
2. Plugins rarely get updated... they'll sell you a new version at a discount but UA figures that they got it right out of the box until the competition comes along and one ups them... then the old plugins get tagged as legacy and a new version is announced. They will update for compatibility with OS releases but don't expect a wet/dry knob to suddenly appear. If it isn't there when you buy it, it likely won't appear even if requested by many users.
3. In cases where we can do a direct comparison from a DSP based plugin to the equivalent plugin from the same company (yes they null they are exact) the native performance of the same plugin is far superior in terms of instance count. The sharc chips really are inefficient. To be specific a/b any number of the Brainworx plugins that can be purchased in native VST format and which are also available as UAD-2 plugins and you'll see how quickly the DSP gets used up.
4. If you like UA plugins for dynamics (and they are very good)... you won't get side band compression. No VST 3 means no side-band in many DAWs.
5. Whether you buy a plugin at full price, or in a bundle or on sale it will be more expensive than the native competition in most cases.
6. Earlier UAD-2 cards, the solo, duo and quads are not universally compatible with the new Ryzen motherboards. Support is hit and miss. Some motherboards allow the older cards to be slotted into pcie ports that can be configured as 2nd gen which makes some motherboards work. Some companies ASROCK for example have released bios updates that will allow the older UAD-2 cards to work. It is hit and miss. Do your research otherwise you'll be trading in your UAD-2 cards for a loss and buying an Octo card which is not effected.
Other Pros
Still some of the best reverbs on the market.
Unison technolgy is impressive
The Avalon SP737 is indistinguishable from the hardware as is the 1176 and LA2A and the Moog Filters plugin is spot on. I have the hardware here.
If you want to monitor through great quality plugins with low latency and need an interface their Apollo interfaces could be the answer.
When would I buy...
1. In some cases if you are trying to postpone buying a new system... off loading the CPU drain to the UAD-2 DSP could be good value if you got your card and plugins second hand at a good price.
2. If there are specific emulations that you feel are best done on the UAD-2 platform you can trial the plugins for 14 days which will give you ample time to compare them to the competition.
3. If you have issues that you need to resolve I have found their support to be excellent. I have had some plugin "choice" options when buying a bundle made available when I called with a specific request. In short... they will work with you to make you happy within reason.
What to watch out for...
Their marketing is almost always impressive. You feel like one of the big boys/girls when you join the club and the comments and reviews in the forums give evidence for this. Don't get sucked into that kind of hype. The competition is fierce and there are in many cases alternatives out there that are as good or better in terms of sound and when it comes to the disadvantages I mention above - it could be a deal breaker.
Some of their plugins, namely the updated compressors, give a volume boost which can be deceiving when assessing the quality of the emulations.
If there is a plugin that has a native counterpoint from the same company ... get the native plugin version - it will likely be cheaper and will allow you to run many more instances relative to the DSP dependent instance counts you'll get on the cards.