Quick update: the Comcast/Xfinity device and the Third Reality device from Amazon showed up today, and the Comcast (Universal Electronics) is very nice (all things considered). It does use a 2450 battery instead of a CR2 (which @jtmpush18 mentioned), but other than that, it's similar in size to the Samsung Contact Sensors, and roughly half the size of the Third Reality sensor.
It joined first time, in just seconds, and using the Add Devices Wizard, I selected one of the Generic ZIgbee Contact sensors -- as it turns out it also has temperature. Extra points.
I installed it on the inside door frame, and while the magnet is installed at an odd angle and decidedly not according to the handy instruction sheet, it works perfectly!
It'll be interesting to see how it compares in terms of battery life to the Samsungs and some of the others I've ordered. Same for reliability, both mesh wise and operating.
I ended up ordering 5 more of the Comcast/Xfinity/Universal electronics units as they just worked, and being similar in size to the Samsungs makes using them for 1:1 replacements pretty appealling.
However: I received a Zooz ZSE41 Zwave sensor in the mail today, along with the Aqara door and window sensor -- and I must say, both of these are crazy small, particularly the Aqara, but the Zooz is very similar in size, and would be a handy replacement for the Zwave door sensors I'm using now.
I think the Third Reality, with it's two AAA batteries might be suitable for a garage door contact sensor, as who cares how big or ugly they are in the garage? -- so if my 4 year old Monoprice tilt sensor gives up the ghost, the Third Reality might get a job!
Of course, battery life on any of these is an open question, but given both @waffles and @kahn-hubitat have had good experience with the Comcast/Xfinity sensors, I figured at $12 each it was worth it.
On a side note, I'm really reluctant to hook the Aqara up to my network. I have ZERO Ikea repeaters, most of my repeating Zigbee devices are GE/Jasco/Honeywell outlets/light switches -- which makes me very nervious given the historic Aqara/Xiaomi Zigbee weirdness.
Well, I don't think it will hurt your mesh to try it. It will either pair and stay paired, or it will fall off the mesh in a few days. If it falls off the mesh, just remove the device.
-- so if my 4 year old Monoprice tilt sensor gives up the ghost, the Third Reality might get a job!
