A stretchy hooded top that functions equally well as a midlayer in mixed conditions, or a stand-alone layer when the weather's warmer, the Aiguille is great when you want the simplicity of a technical long-sleeved t-shirt to keep off the sun or cut out a bit of breeze, and don't need anything too warm or heavy. Though aimed primarily at climbers it has a do-it-all versatility, and I've happily worn mine cragging, scrambling and hillwalking. It'd probably be good for running, even.

In use

You don't get much insulation out of an Aiguille, and in terms of weather performance it's better regarded as a slightly beefed-up baselayer/t-shirt than a softshell. On windy mid-teen days I've boosted my insulation on the go with a gilet over the top, a pairing that works well. 

Light (my size L is 295g), breathable and comfortably soft, the Aiguille is a wear-all-day sort of top that you can pretty much forget you've got on, in a good way. Even working hard in the sun I've not found myself getting hot and sweaty in it - in fact one of its suggested uses is sun protection on glaciers. But though it's pretty cool for summer I wouldn't say that comes at the expense of toughness, and it certainly feels well made enough to handle some abuse when climbing or scrambling. 

It packs down small too, about the size of a grapefruit, which makes it ideal to chuck in your crag pack as a just-in-case extra layer. I think it'd be spot on for weight-conscious backpacking and mountaineering.   

Fit

The Aiguille comes in both men's and women's sizes. Its slim cut works well within a layering system, fitting fine over a short sleeved t-shirt. If you need extra warmth then you'll be wearing it on top of the Aiguille. There's plenty of length in the arms, and cut-outs for the thumbs to provide more wrist coverage; I find the size of these holes too small for comfort. If you like to be able to pull your sleeves up to vent your arms, you may consider the cuffs a tad tight, too.

Hem length is OK, with the proviso that I often seem to find Mountain Equipment tops come out a bit short in the trunk on me. It's a simple hem with no drawcord, which is spot on for this minimalist layer. Unfortunate for a climbing top, I get loads of hem lift with raised arms, suggesting the tailoring could be better. This hasn't been an issue when wearing a harness, but for bouldering or scrambling without anything around the waist to hold it down I suspect it could get irritating. If you try one on in a shop it's worth doing the arms-up routine to see if the hem is an issue or not for you.    

When it's breezy the collar gives a degree of neck protection but I imagine it'd stand up better as a plain collar without the weight of a hood. With a deep zip, you can get a lot of air in to cool down on the uphills.

The tendency to put a hood on every item of clothing is not one I can get behind, since it makes for a bulky feel when you have several hooded layers on at once. While it helps keep the sun off your head or your ears warm around camp, the Aiguille's hood is too loose to fare well in the wind, though worn under a helmet it works OK. Hoods have their fans but personally I'd prefer if the Aiguille came in two options, hoody or hoodless, and my own preference for this particular piece would definitely be the latter.  

Fabric

I really like the stretch jersey fabric, which has plenty of give for freedom of movement and at 175g/m2 offers the ideal weight and thickness for this particular top, which is clearly not intended to offer much insulation. It's best regarded as breeze-resistant rather than windproof, taking the edge off while still allowing enough air flow to remain pleasantly breathable and quick-drying. 

With its flat seams and soft inner face, the Aiguille can comfortably be worn as a base layer next to the skin - I wonder if it might work well like this in winter, but I know that hood would annoy me.

Ethics and environment

It's made in a Fair Wear Foundation audited factory in China, and backed by ME's Product Lifetime Guarantee, which defines 'reasonable life' as the time a product could have been reasonably expected to last when subjected to normal wear for its intended use.

Summary

I'm not keen on the hood, and the cut could clearly be better on me; but despite this I really like the Aiguille, which has found a niche in my wardrobe I didn't know I needed to fill - the long sleeved t-shirt with attitude. Lighter, cooler and more breathable than a typical softshell or micro fleece; not as wind-resistant, but tougher and stretchier than your average windproof: this thin top is so versatile it'll suit pretty much any mountain activity, and fares equally well worn next to the skin, over a t-shirt, or within a warmer layering system. The price tag might be considered a stretch, but given how often you are likely to wear it, maybe not...