I don't like stuff like this on a bike.....it's part of the dumbing down process to me.
The biggest risk is that someone gets on the bike at lunchtime in January, takes a peek at the temp gauge and thinks "it's ok, it's 9 degrees now' and gets lulled into riding like it was April and 9 degrees.
That's WRONG, and dangerous......nobody needs a temp gauge to tell them it's cold, but having one and riding as above......the most likely outcome is that you'll be off on a patch of black ice in a dip or under some trees, because the risk assessment part of your brain has been deadened by knowing that last time you looked at the external temp, it was several degrees above freezing.
Riding (and to a lesser extent driving) should never depend on artificial aids that can easily lead your brain astray......it should be based on common sense, gut feeling and experience, what you can see, smell, feel, even taste (diesel in the air TASTES!) and regardless of how cheap a farkle is, it's a DANGEROUS thing if it has even the slightest chance of dulling your common sense.
Sorry to piss on your cheapo bargain idea, but I can't see a single reason why you'd want one