Trouble was fine with a collar, so I bought THIS feeder. Note, prices vary, shop around. Also, be VERY careful ordering one of these things on Amazon. As I browsed I saw some really blatant listings for either knock-offs or fake listings of identical feeders. Like, 7 or 8 per page.
With the lid stood open Trouble would eat from it no problem. As soon as I added the sensor tag to her collar and turned on the feeder she clearly decided it was EVIL and had to be killed (she repeatedly swatted the moving lid). I could wait for her to adapt to it. Or I could play around with it.
In THIS video the guy explains how he swapped the feeder controls so that it stands open all the time and CLOSES when the tag approaches. This would allow me to put the tag on Shadow, and not care if the moving lid freaked him out. Note, this modifications require a soldering iron and a screw driver, but are otherwise very simple to do. This modification would also fix the issue mentioned in the reviews where the unit sometimes loses the tag while the cat is eating resulting in the lid trying to close on the cat.
The collar is now on Shadow, who decided I was torturing him by putting this THING on him, and Trouble is back to happily eating out of the feeder.
There’s one other issue mentioned in reviews. Some tags don’t seem to close down tight enough, with the battery in them, to actually work properly. The tag included in my set initially seemed to have this problem. I fixed it by removing a plastic ring gasket from inside the tag. I assume that the tag is now no longer water resistant, but since my cats are indoor cats I can live with that.