Of all the Sony-E-to-Leica-M adapters on the market, the new Voigländer VM-E close focus is the best option but also the heaviest. As well as allowing you to mount manual-focus M lenses on the Sony A7s, the VM-E has a nifty trick to keep you amused. It incorporates an additional focus ring that can be used to achieve a minimum focus distance of under 30cm. In contrast, most modern Leica lenses will not focus to under 70cm and some, like the Noctilux, have a minimum distance of no less than one meter.
The auxiliary focus ring is kept in check by a slider. When you need to focus closer than the lens is used to, it is a simple matter to flick the slider, set the lens to its minimum distance (typically 70cm) and then use the auxiliary focus ring to home in on the subject. It works as advertised as long as care is taken to achieve accurate focus and does takes a bit of practice. For many Leica lens owners this additional facility will be worth the premium price of the VM-E.
Quite apart from this wizardry, the Voigländer is extremely well made and clicks into place at both ends with reassuring accuracy. It is about 2mm wider than the Novoflex NEX/LEM which is a no-frills adapter with no fancy tricks. On the other hand, it is much heavier at 120g which is a significant addition to the weight of lens and camera. The Novoflex is a relative lightweight at only 35g. On balance I would say that in quality the VM-E is even higher than the Novoflex which is usually acknowledged to be the premium third-party brand. However, you have to weigh up the extra 85g of weight and whether or not you will actually use the close focus.
As you see from the above photo, the adapter (any adapter) adds about 1cm to the overall depth of a lens. In the case of the Sony, this is exacerbated by the gold collar which is, in fact, part of the camera and is used to achieve the optimum distance between lens and sensor. It is a penalty of having such a thin body. Focus is achieved by moving lengthening or shortening the distance between the sensor and the lens.