The 2-way splits the discharge between two sides and closes the other two. It is the middle option in the family and, for most desk-under-a-diffuser complaints, the one that solves the problem without creating a new one.
Half the air one way, half the other, which means neither stream throws as hard as a 1-way does. You get the air off the person without turning it into a jet somewhere else.
Standard body: 24 by 24 inches, 2.75 inches deep, polystyrene, held on magnets against a compatible steel grid or diffuser face.

What does a 2-way diffuser cover do?

It opens two sides of the discharge and closes two. The supply volume is unchanged, but instead of spreading in four directions or firing out of one, it leaves through a pair of openings. Each stream carries roughly half the air, so it travels further than a 4-way spread but nothing like as far as a single-side 1-way. That middle setting is why this configuration suits so many ordinary complaints.

Should the two openings be opposite or adjacent?

Turning the cover decides it, so think about the room. Opposite openings suit a corridor, a long table or a run between desks, pushing air both ways along an axis and leaving the two flanks clear. Adjacent openings suit a corner, sending air into the two directions where the room actually opens up while closing the sides against a partition or a wall. Both are the same part, so the decision costs nothing but a moment's thought on the ladder. Work out which you want before fitting, then check the result from where the complaint came from.

Why pick 2-way over 1-way?

Because a 1-way sends everything one direction, and everything is a lot. Full discharge through a single opening throws hard, and on a diffuser with decent supply pressure that can create a draft fifteen feet away that nobody asked for. The 2-way halves the throw in each direction. If you have two reasonable places to send the air, splitting it is almost always the more comfortable result, and you are less likely to be back on the ladder. The same logic runs the other way: if only one direction is genuinely usable, splitting the air sends half of it somewhere unhelpful, and the 1-way is the better part.

Will it fit your diffuser?

The same three checks apply across this family. A nominal 24-inch-square diffuser, which is the standard ceiling grid module. At least 2.75 inches of clearance below the ceiling line for the depth of the cover. And a steel attachment surface, because the magnets need something to hold on to. Aluminium grids and painted plastic faces will not work. Test with a fridge magnet before ordering, and measure rather than assuming, because a tile that looks like a standard module can be an odd size in an older fit-out.

How does it install?

Offer it up, let the magnets take it, with the two openings facing where you decided. No tools, no fixings, nothing to make good afterwards. Orientation matters here as much as it does on the 1-way, so after fitting, stand in the spot that prompted the complaint and feel what has changed. If it is not right, lift and rotate. That is a ten-second job while you are still up there.

Does this change the system balance?

Barely. The outlet still passes the same volume, so the branch behaves much as it did. What changes is where that air lands and how far it carries. A single 2-way cover is a comfort adjustment. If you are fitting a dozen across a floor and redirecting most of the supply on a branch, mention it to whoever maintains the HVAC, because a lot of small adjustments add up to one noticeable change.

Is this a filter?

No. It redirects air and nothing more. No filter media, no MERV rating, no filtration claim. If the goal is cleaner air rather than better-aimed air, that is a different product.