I use a Cycleops 400 pro at the work gym and have a Stages gen 2 with left only on the bike itself.
I find indoors on the real bike with left-only Stages is my lowest reading, by far. Then it's a tie between the Cycleops indoor and the real bike outdoors.
My fluid doesn't have a flywheel at home, and you feel it. That Cycleops stationary in the gym has a good sized flywheel, and uses said flywheel for resistance also. There's a little wiper thing and an arm that applies pressure to it.
The "feel" of the Cycleops stationary is light years better than the dumb fluid. If I had $800 laying around and fancied sleeping on the couch a while, I'd buy a smart trainer. I HATE HATE HATE the feel of my fluid. It's easily about 20w lower reading on the Stages on that fluid. I routinely have to alter my power targets for workouts on that. So I do my workouts at lunch at work when I can, to use the nice rig.
I find climbing power vs. indoor on that Cycleops is very close. TT? I don't do it enough to have good adaptation to the position to lay out the same power.