The Apollos are well made, sound phenomenal and the UAD plugins ARE excellent and quality wise in many ways above all but the best of native plugins.
That said, RME gives the best driver support out there, their hardware is rock solid, and their stuff is feature rich.
UAD doesn’t allow for midi control of their Console app (except with the Softube Console 1), no direct-to-disk recording without a PC attached (big feature on the UFX), MADI is available only on the Apollo 16/x16 and due to the thunderbolt protocol, it isn’t compatible with AMD Ryzen processors. RME does all of those things better.
UAD interfaces have the mentioned Unison feature which is cool, and a neat thing is that you can “preload” plugins into all your channels in Console, then unplug the interface and use it as an FX box in live performances (plugins remain active even after removing the computer).
I own an Apollo 8 and it is no doubt a premium interface. I originally wanted the RME UFX, got scammed trying to buy it online, finally decided to go to a music store and buy it there where the sales person(!) swayed me over to a UAD Apollo last minute. I love my interface for its quality sound and quality make but I am annoyed with UAD with what to me seem to be arbitrary & poorly explained limitations (eg no standard midi control of Console) and a customer service / after-sales service that is smug at best (just check their forum and have a look at the way the “community” and their staff handle criticisms or feature discussions).
Also, UAD’s pricing policy with their plugins is sort of designed to make you addicted to buying their stuff - not even kidding.
When I first got the interface, I bought one or two Unison plugins that I really wanted - the first few, time-limited coupons started coming in from UAD. My first coupons coincided with one of their yearly sales, so I used them to buy a few more plugins. With each purchase I received one or two(!) more coupons, so I ended up buying quite a few things for what seemed like great deals.
Of course paying 149€ for a plugin is going to seem like a great deal when it’s standard pricing is set to 399€…But who buys UAD plugins at full price?! Those prices merely serve the purpose of normalising spending on their plugins.
Eventually as I spent more, I received less coupons but my tolerance for spending on their plugins had by now gone up. It took a phase of extended traveling (without my equipment) to veer me off their marketing traps again. I’m convinced that UAD plays it exactly like that (it’s their strategy), and to me that is quite a turnoff.
I’m also mildly bothered that UAD doesn’t give the option for commercial clients to recover VAT on plugin purchases.
Now, this is not meant to be a rant against UAD and I’ll say explicitly that I am happy with my Apollo - everything it does it does extremely well. These are just some of the things I wish I knew before I bought into their ecosystem (probably still would have gone for it, only would it have saved me some of the disappointed expectations down the line).
If I’d have to make a choice today again, I’d probably go with a UFX+ as my hardware collection has grown since & I work and create more OTB today than I did back then. The UFX+ has a few features (midi control, disk recording, better routing) that are more suitable for that use case scenario.
But who knows, maybe then I’d miss the sound and the plugins of the Apollo? lol