Thanks to a poster above - and thank you, poster above! - I read through the 9550 thread and decided to try one out.
I recently bought the Zenith 901, so this is my second coupon purchase.
My "big" TV is an older 31" RCA CRT SD, connected to the box with coax and A/V cables, so I won't try to compare picture or sound quality between the two boxes. They both look great, much improved over analog.
Points of interest:
The 9550 is now Energy Star labeled. So far, no temp issues, even after 4 hours constant on. The Radio Shack kid wrongly assured me that the 901 is not - confirming that you have to do your own research if you want to get the facts.
Running from the same rooftop combo antenna, I was surprised to see that the 901 picks up a station when connected to my bedroom TV - a bottom line 19" Phillips with only coax connection - that it wouldn't on the RCA. Meanwhile, another station that came in well on the RCA through the 901 sometimes breaks up on the Phillips. Go figure. Too many variables to say why. The RCA is connected to an amplifier/splitter, so that could be it. Or does the TV's internals affect a converter box's performance? I don't know.
I think that actual A/V performance is hard to gauge on my sets. Maybe time will reveal more differences. But I'd give the clear convenience edge to the 9550 so far:
Much better extended program guide.
Faster channel change via remote, although actual implementation is delayed on both boxes, and probably takes about as long. (There is a mildly bothersome electronic "click" on the 9550 when the new signal comes in.)
Much faster box volume control on remote.
TV volume control on remote.
Remote larger and more convenient. (901 remote will disappear into any gap in our seating.)
Signal Strength uses color band and numbers - much preferred.
Zoom feature terminology is more understandable: "16:9, 14:9, Zoom, Anamorphic".
901 is "Set by Program, Letterbox, Cropped,Squeezed."
Much more thorough manual (such as explaining the options above).
Other points of interest:
Just from tooling around (haven't thoroughly read either manual), it does seem that while you can speed up the 901 lock on a new channel by hitting the central, round button, this may slightly speed up the lock on the 9550, but it also brings up the display, so you have to hit it again to turn that off.
On my coax only Phillips, where I have to use channel 3 rather than Input to employ a box, it appears that the 901 has the effect of degrading the antenna signal strength. Normal reception is better without the box in the signal path. This didn't seem to be the case with the 901 and the RCA, where I use Input to go from analog to digital.
I haven't tried this with the 9550 on the same TV, but I'm guessing that it has more to do with relying on coax only than with the box itself. But this could matter to some, because Pass Through on the 901 means turning the unit off, where the 9550 has a button on the remote for this. If you're using the Input button, I don't think any of this will be a factor.
So far, I'm very impressed with the 9550.