The Orthos Prime's polarity for its Stance slot makes it ideal for slotting in Shimmering Blight immediately. While the Orthos Prime can also use Bleeding Willow, its polarity will reduce the number of its bonus mod capacity, unless changed using Forma.
The Orthos Prime (and its normal counterpart the Orthos) has a unique equipped normal attack animation where it performs thrusting and stabbing attacks against an enemy. This attack is completely replaced upon equipping either of the polearm Stance mods.
New Loka asks for an Orthos Prime Blade as a sacrifice to become Pure (rank 4). Be sure not to trade them all away if you plan on ranking up New Loka.
This weapon used to have the same stats as normal Orthos. It was buffed in Update 9.5.2.
Note that the end-blades are not mirrors of each other and seem to have shapes that could fit together. The blades are asymmetrical.
In real life, Rubidium is an alkali metal element that is very soft, ductile and silvery-white in color.
It is not good for a blade as it's not hard enough to scratch other materials. (Brinell hardness of 0.216MPa, thousands of times worse than iron, which has 490MPa).
Being ductile, it is also easy to bend, so it won't keep an edge (or any shape for that matter) when striking an object.
Rubidium, as with most alkali metal (like Sodium), oxidizes violently when coming into contact with water, sufficient to produce a small explosion.
This could possibly relate how it can inflict a Blast proc, even when contacting land.
It can spontaneously combust in air, so it is usually stored in sealed containers with an inert liquid (mineral oil) as a buffer.
Despite the Orthos Prime's description, Rubidium is actually denser than Iron, by ~53%.
Rubidium has useful properties in laser science, atomic clocks, nuclear physics research, and solar panels. This can lead to speculation that the "rubidium" in the Orthos blade is either some kind of engineered material or it is used to focus/channel something.
It is also possible that Rubidium in the universe of Warframe is based on Rubedo, and therefore a different chemical or material altogether.
Along the blade reads the text "The longest arm is the law," written in the Tenno alphabet. This might be a hidden joke, referring to the Orthos Prime Handle being substantially longer than the Orthos' handle.