Plasterboard Corners

Does it specifically have to be plastic?

If metal will work, then have a look at the Expamet site. They have a range of metal plasterwork components that can be cut and bent.

not specifically, but it has to be as thin as possible, with no "ridge" on the corner liek you get with normal plaster beading ad I wont be plastering the plasterboard once done, I will just be feathering in with jointing compund so the corner strip needs to be thin enough to be easily covered and hidden by the compound.

In that case, tape may be a more suitable choice.

What about plasterboard tape as a last resort?

Yes I agree.

One could use the fibreglass stuff as long as it was being feathered out to the nearby surfaces, but paper would require fewer coats

Can it be that difficult to bend the standard bead? If the corner's going to be straight and resistant to knocks, I don't see there's much option. IIRC the smaller bead is only about 2mm so doesn't affect the levels significantly.

No it's not it bends rather too easily...

If this is an external corner it'll need something to take the knocks, IMHO the only thing that do that is metal. The grid goes behind the board and only the bead is at the surface. Get the right stuff for your thickness of board and you'll just have gap to fill and bead to board to feather.

It depends on the material and the angles involved.

Then it becomes an issue of blending the edges so that they disappear

If you must have a bead in this case, use right angle and cut one side off it, leaving a corner bead and one flat bit. You get an invisible result you will need to cut away the paper on the board under its edge though, then fill right over on one side, and up to on the other.

Well it is, but if you haven't done it before may seem insurmountable to the point that one will seek alternatives.

The trouble with a corner is that imperfections stand out like a sore thumb from any angle, and in any light. Imperfections on the face might catch your eye now and again