The Boyu air curtain I own is just like this one only black. I believe it is about 7 years old. Like the one pictured my air curtain is about 12" long but they can be bought in a variety of sizes. After having it this long without any loss of performance, I must say I am very pleased with this item. I believe I paid £6 minus my 15% discount, for it, but could now buy one 3x that size at Amazon for the same price.
The air curtain is basically just a hose with hundreds or thousands ( I am hardly going to count) of very small holes to allow air escape. Plugged into to any air pump this makes a line of bubbles, or curtain effect which is normally positioned at the back of the tank. This creates a nice effect on it's own, but if you happen to have a coloured led light, or better yet, lights you can really creates a lovely feature as the bubbles catch the light beautifully.
I have used this in both tanks, most recently in my sons tank, but removed it to make way for his new volcano. We also had it in the large tank with led's for sometime and I found some of the fish native to fast moving waters would delight in racing through this. I am currently looking for a new set of led's as we had trouble with the last. If I find new led's it will go back to the large tank.
We try a couple of other applications with this, but with less success. The first was around a large crystal type ball we once kept in the tank. It looked awful rather than accenting the ball it obscured it. Next we tried it in a cheap plastic volcano. The air seemed to accumulate and come up in big bursts which dislodged the volcano. We also tried placing this in a sunken ship ornament which was not too bad, but the line effect of bubbles was unnatural. Worse than that, it chased the fish that used the ship as a hiding place out, and the fish who would have enjoyed the extra current from it had no use of it tucked away like that.
So while I have heard people claim it works brilliantly for some ornaments, I have not actually seen it, and in my experience it did not.
In spite of this, I am giving this a full five stars, used as it is meant to, as just a row of bubbles it looks nice. Lit up with additional lighting it is beautiful. When I used this with a colouring changing pond light it was like a mini light show in our fish tank. In addition it provides extra oxygen for your tank.
I would recommend this with a small air pump, a 50 or 100, but it is more forgiving of a bit larger pump than most air features. Also while the bubble will extend a bit past the length of this hose, and I have and will use it in the large tank, a bigger curtain would be even better for the big tank and ideally I would shoot for one 2" under tank length.
Also - this is just a personal opinion, but I believe this feature works best without other air features in the tank. One nice sheet of bubbles at the rear of a tank, perhaps radiating colours from led lights is really nice.
A pile of items spewing bubbles at once looks cluttered and artificial to me, but you may think differently.