I too have a Saris bike carrier like yours. I agree exactly with all your points including the potential for problem rust areas at the "lock" slot where the hold down arms clicks in (and where it clicks into when in the "down" position). The release button is a little stiff at times too, I imagine some silicone spray might help.

As for the mechanics of day to day use though, I'm 90% happy. Real easy to get in and out assuming you can lift your bike up to hitch level+. Heavier bikes might present a problem. Clamp arm has never caused me any concern. Do remember to put the locking pin in before you drive off I forgot once and it could of been nasty if a fast stop was called for, as it was the not so gentle bonk on my rear window was sufficient to make me not forget again

One small issue is that mixing a mountain bike or a cruiser with my bike (hybrid/flat bar roadie) when two-up required me to adjust the MTB seat to avoid my handlebars. This could be specific to my particular combination of bike types i.e. two drop handle bikes would probably be fine.