My M6 is hardwired and in park mode it does not get hot, even when its been on all night.
UPDATE: I made this post when the weather was cool and under those conditions, the M6 works fine. However, on a sunny day the M6 gets very, very hot and as others have mentioned, goes into some kind of spasm, will not record and repeats a phrase in Chinese. When it cools down, it works fine. Clearly there is something seriously wrong with the design and I do not feel confident using it on a hot or sunny day. In fact I now take it out and no longer use 'park mode'.