The Glacier 5.0 from Mountain Equipment is focussed above all else, on comfort. It is the brand's deepest, warmest and 'most comfortable' mat, so it should come as no surprise that it is a chunky beast.
It is certainly not designed for fast and light backpacking or lightweight bivouacs, but even accepting that, the pack size is pretty big; longer than some small tents and certainly more bulky than most sleeping bags.
But it won't fill your car boot, and car-based camping is where this mat excels. I was on the road for over a month in the chilly autumn, with a large tepee tent for a bit of extra comfort, chairs and a camp table upon which to cook with my double-hob stove, and this mat suited that upgraded set-up perfectly.
It's tricky to judge the effectiveness of the insulation when so many other variables are at play, but the comfort was never in question. At 5cm thick, the Glacier 5.0 is as close to your own bed as you can reasonably expect to pack for any trip. That old adage that nobody sleeps well on the first night of a camping trip went straight out of the canvas-covered window.
At 1200 grams it will be purely down to personally choice whether it's worth hauling this mat to any remote base camp (as per Mountain Equipment's recommendation). But then every expedition needs its little luxuries and good quality sleep should be high on that priority list!
Whether this mat is considered good value will also come down to how highly one values sleep; cheaper mats are available, even ones of comparable spec, but the quality of the Glacier 5.0 shines through.