I do use it as a DSP accelerator for UAD plugins though. My Apollo is rarely used as an interface these days, though it’s a great way to access portable low latency tracking for a Townsend Labs Sphere, having the required two digitally controlled preamps and a UAD DSP version of the Sphere plugin.
If it had Loopback I’d probably use it as my daily driver but my reliance on loopback is more about being a blogger than it is about being an engineer. The provision of 4 discrete headphone mixes, driven from the Pro Tools mixer is a major win for me too. It’s not an expandable solution but for the tracking I do Carbon with some additional mic preamps connected via ADAT is all I need. The Avid Carbon appealed to me immediately on its release as I am exactly that person who wants the latency free tracking experience from within Pro Tools that Carbon offers without the complexity and expense of HDX. I love its quality, ease of use both via the rednet control app and from the front panel and the ease with which I can route audio via its loopback facility. I bought this largely for its Dante capabilities but I’ve not really followed through on that, particularly as I’ve now got a Carbon for tracking sessions. My principal interface for day to day work is my Focusrite Red 4 Pre.