This lens was hiding in one of the boxes under the Christmas tree and I was really curious how it performs but it took a while to have a general impression (mainly due to bad boring weather and work). I unfortunately left this converter home when I traveled to a recent trip to Thailand.This converter was designed for the SEL16F28 lens and it has a 0.75x factor so it makes the wide angle 16mm lens ultra-wide (around 12mm, equivalent to 18mm on full frame cameras). It's specifically designed for this pancake lens, so it doesn't deteriorate its optically quality much. Some cynic would say that it's hard to further spoil it. Although most of the SEL16F28 reviews were very negative, I was satisfied with this cheap lens. It served me as a small pocket lens and I also managed to take some fantastic shoots when it was paired with the vcl-ecf1 converter. Stop down to f/8 and it's quite good. If you already have to 16mm lens I recommend to buy both adapters. They sell now around 100 euro, which is a steal for a 12mm f/2.8 lens or a good f/2.8 fisheye lens (assuming that you have the 16mm lens). I haven't done a thorough test yet but my initial impression is that it has very good build quality with a nice silver metal alloy and it snaps well to the pancake lens. It's heavier than the 16mm lens (127g vs 65g), but the two together is still light enough and balances well on my small nex-5. It arrived in an elegant nice zip-closed etui.
You can't add standard filters to it but it has a built-in hood. To give an opinion about the optical quality I need more time with it. What is clear that the color fringing of the 16mm lens won't go away by adding this converter (same with the fisheye converter).
Actually I was more interested, how it behaves on the 30mm macro lens (SEL30M35). This combination is much bigger. Below you can see the fisheye adapter on the pancake lens and the ultra wide converter on the 30mm f/3.5 macro lens:
Below you can see few photos taken with this later combination:
The effect is not that dramatic as with the fisheye lens but it gives a bit more space than the 30mm lens would give, so you can show more about the environment when you want to take macro photos. The good news is that you don't have to stop down that much to have sharp results and you still have infinity. With the fisheye converter you can forget sharp far away subjects, so you can't use that combination as standard lens, while the sel30M35+vcl-ecf1 combo is an OK 22.5mm lens (not a good one though). I think that despite the limitations, I will use my 30mm macro more with the fisheye adapter combined.