My problem is not do they work . I have had two given to me and both stolen . Guess they are to tempting to walk by . Just give me a red cup . lol
When I bought my better half one of the 30 oz Yeti cups I took it by a trophy shop and had it laser etched with her name and a design... I'm sure that won't deter all scum sucking POS thieves but I think it helps..........
Three can keep a secret................If two of them are dead! (Benjamin Franklin)