I still really like ours! We've had it since June, and while it's definitely not the easiest harness to tighten I haven't found it to be a reason not to like the seat. I don't adjust it each time though...I just 'chicken wing' him in and out. The buckle kinda stinks, but it's the same one as on other Graco seats. So far it has never gotten stuck.
DS2 is 2yrs, 28lbs, 36inches and fits nicely in it. I also tried him in a Pria which did have more leg room, but he has never complained of being uncomfortable in the S4M and he is very verbal so he would say something if he was. He looks just fine in it...he either bends his knees or stretches his legs up the seat back.
I love the head wings and deep sides. I am big on SIP since my van is older and has no side airbags, and he rides outboard. He sleeps wonderfully in it as well. I like how tall it adjusts and that it is narrow as well.
I've never had it installed FF long enough to try out the harness adjuster that way so I am no help there.