I've seen something about these very recently. I think what you've seen may be from airpropogator.com (USA) or the Rooter Pot (again USA) - or the UK version is a cut down plastic bottle, or even a plastic bag (which is much lighter in weight and therefore less likely to cause the stem to break)

Hi, welcome to GoY, this is a variation on the air layering of plants whose stems will form roots when damaged, all you need to do is make a slit into the stem, [remove a few leaves if necessary], pack the resulting tongue with damp sphagnum moss, and enclose the whole lot in a plastic sleeve tied at top and bottom, when you see roots, detatch from the parent plant and pot up, no need at all for , no doubt expensive, new gadgets, the 'old fashioned ' way, is still just as effective, Derek.

Thanks guys I actually found what I was looking for on eBay Irish air propagater :)