Metal is an excellent temp conductor. Yes it does freeze more quickly. Plastic insulates a bit. It also flexes a bit.The RentACoop one is about 8" tall x 4" x 4", so not too unwieldy in a small coop, but it sounds like you've found something that's working (and that a rat couldn't chew through).
The plastic water containers have held up surprisingly well, but it's that heavier, textured plastic that doesn't shatter when a hole is drilled.
Only the red cover of the oldest waterer, a cereal saver, has begun to crumble. It's 6 years old, seen here being enjoyed in its younger days by Beebs and the extraordinarily missed Frida Bakawlo, One-Wattle Wonder:
Conversely, I've been curious if it's true that metal waterers freeze more quickly than plastic. That's something the internet says, but is it true?
Water expands when frozen. A plastic milk carton filled with water and thrown into a freezer (for a consistent temp) will expand. The ice will also blow off the lid as it freezes. A metal container of the size will get cracked as the water freezes. Any still liquid water will spill through the crack, freezing and expanding the crack as it does. It's why you only fill the water bottle to 3/4 at most when freezing one for an ice pack.
Metal when cold enough will instantly freeze moisture. The movie A Christmas Story has a kid getting his tongue stuck to a metal flag pole. It happens. It doesn't happen at 32F/0C. https://biologyinsights.com/can-your-tongue-stick-to-a-frozen-pole/
Is it likely to happen to wet chicken wattles inside a coop is a place like Bristol....no, it's probably too warm. Could it happen given the right circumstances (extra cold)? Yes. Even a frozen popsicle can cause the sticky factor (as my brother discovered to his chagrin). The popsicle had been stored at about -10F/-23C.
Metal can also cause frostbite through the conductivity. That's why it's extra important to use gloves when handling metal in water in frozen temps. Those temps are a bit warmer than the freeze the moisture on your tongue, but not a whole lot warmer. A couple degrees below freezing isn't going to do it.

