LS9 can be a bitch to get around really quick even if you know it pretty well for certain tasks. Phantom power, getting to compressor attack and release controls, things I use a lot need for one offs to be navigated to on a little screen. Turning Q knob to the left turns the Q up, but using the big encoder RIGHT next turning it left turns it down. Layer / fader / menu system has me in the habit of clinging to the home button annoyingly. Setting up mute groups and tap delay is annoying if you are starting from zero in a run off. "flex 15" graphic EQs are often fine but sometimes not, and its then when you care. Compressor is hardly transparent, preamps are a little cold and harsh. Output cards are 16 i/o so you need 2 anything to get 32 ch for Dante or something. The gain knob is positioned right by the top edge of a protruding screen, and I've known more than one person to lob it right off putting a road case back on. I think every engineer who I've walked through this console for the first time has repeatedly gotten confused about the ambiguously color coded toggles for various bypasses and such.
I do really like the LS9, despite all of this. Especially for touring acts, the customization abilities like the UDK and the custom fader layer are huge and speed problems for accessing certain controls are less irrelevant. But, I think for guys doing lots of one offs, different acts and etc there are plenty of downsides to it. The SI gives you tons of controls with their own encoders right on the surface so access to attack, release and phantom power are super quick. Encoders above channels let you manage HAgains / hpf / and pan super fast, great for one offs or time pressured circumstances. No arrowing around looking for something on a tiny, low res (!!!!!!) screen. "toggle" style fader / layer system eliminates the leash to the home button. Fader glow sounds stupid, but especially if a variety of skill level users will be op'ing the console it really helps those "where am I?" moments. Full graphic EQs on every output!
All in all, one console does not fit all, but IMO the SI compact is a better fit for some users than the LS9.