Erick
I have had this unit for one month, if that. It was purchased used from Breanda (Thunderchilddobs).
In the first few times that I tested it out I only ran it on a low setting (as per advice from Humayun down here in Canberra, as I heard it runs the batteries flat otherwise, or can cause the air around the scope to bubble). It was hard to tell if it was working or not as there was a slight breeze which helped the dew situation. We had a big frost this week and that's when I realised she's stuffed.
I'm a fiddler, so when the unit arrived I opened her up to clean out the dust and inspect and I saw the brown spot, but assumed it would be ok b/c the unit does produce heat, and it's used. Turns out I was wrong...
I have never felt any warmth from any heater what so ever. It was shipped to me as it currently is....