I have to admit, I agree with the use of that 'figure of speech' (also 'tows like a dream' ;-)) - it doesn't tell you anything useful.
When I was looking to buy my first van and towcar recently, I just kept reading 'tows like a dream' and 'can't even tell the van is there' - doesn't help you in trying to decide on what to get.
When I finally bought my car and did my first tow, I was amazed at how glaringly obvious it was that I was towing a caravan - apart from the constant tale-gater, acceleration was non-existent and the corrugated iron that sometimes pass for roads in this country regularily reminded me that I was towing something.
Unless you're towing a bicycle with a 32-ton arctic, I could never imagine using the 'figure of speech' of 'I can't even tell the caravan is there' - it's just not even vaguely accurate!
Gotta go - still got this months 'Pedants Periodical' to read ;-)