You absolutely can not go wrong with this interface. It truly brings legit studio quality in any house/setup at a tiny fraction of the cost of a studio console.
I don't have much to add on top of what most reviews say about the SSL 12, or rather the amount of praise it gets. It's all justified and real from my point of view. It's built like a tank and it performs like a race car, simple as that.
In every technical aspect it really outperforms many interfaces which can be even 2-3x more expensive. The drivers are reliable and the extra software around it with all the extra functionalities delivers in essentially every aspect.
My only "complaints" are ultra nitpicky details like:
- the knobs are just plain ugly and being plastic doesn't make them look any better, I am so done with this ultra ugly aesthetic of many brands that make studio gear. This mentality that ugly inspires a professional look is a tired and outdated trope.
- the metering could be more accurate, but I guess it gives you something to look at. It could definitely be improved, but if you're relying solely on those to check things, you have bigger issues.
- the form factor is very comfy and practical from a workflow perspective, but a nightmare if you are OCD with keeping stuff clean like me. I'm aware there's a "deck saver" for it, but I think that 40 eur for a plain piece of transparent plastic is beyond outrageous and it should be included by default in the package.
The only other real competition of the SSL is the equivalent MOTU in terms of functions and I/O config and price bracket and at that point it's really a matter of preference in relation to size/form factor and whatever else.
