I think some people are confused about what a representative on mission was.
They were civilians with extreme oversight, supervision and direct control of the military.
It was the very deputies of the Convention, - the elected members of the Assembly - being sent to the front lines not to play soldier but to keep an eye on the officers for any Cesarist impulse or treasonous whim. They were all obsessed with the fear that someone would rise as a Caesar - and they were right to be. Both Robespierre and Saint-Just warned against celebrating military victories so it didn't inflate the ego of any general. The reason they debated battle plans with generals is because they wanted to keep a firm legislative control on military operations.
Remember what you might have heard about at one point in class, the three branches of government: legislative, executive and judicial? The Convention had literally decapitated the executive (that was the king) and left that seat vacant, then drained the powers of the ministers, who they no longer trusted, and transfered them to the Committee of Public Safety. The CSP emanated from the legislative but acted like a de facto pro-tem (temporarily appointed) executive. (Important note: the CSP had power over everything but the police i.e. who was arrested and sent to the Revolutionary Tribunal - it was the Committee of General Security who was in charge of that, which was the source of tension with the CSP and led to a crisis in late Spring/early Summer 1794.)
(Nowadays, executive power is usually in the hands of either presidents or still of monarchs in parliamentary monarchies though it's mostly symbolic.)
According to Michel Biard, there were 426 representatives of mission (out of a total of 749 deputies in the Convention). (See here Annexe #1, p. 1.) Almost everyone on the CSP but Barère and Robespierre were sent on mission. Saint-Just had the same amount of power as his colleagues. I know that he and Le Bas were sent "extraordinarily" in Alsace but I would need to check what that actually meant legally for the other representatives operating there - as in, if it actually impacted their powers. However, I know it means Saint-Just and Le Bas had discretionary powers that superseded the local authorities in Alsace and the standard military hierarchy. The Committee of Public Safety, invested by the power of the Convention, made decrees that sent the representatives, usually in pairs, to every département or region currently ravaged either by the external war (the English, the Prussians, the Austrians, etc.) or the two types of internal war: 1) the Northwestern départements i.e. the Vendée and Bretagne regions and 2) the federalist insurrection caused by the Girondins ex: Lyon. They were given the power to take all measures to ensure the salvation of the Republic. It was essentially a state of emergency mandate. The Terror was one for Paris in practice and all of France in theory: since it was actually extremely hard to have centralized power in a time when communication circulated by the speed of a horse, the representatives on mission had the mandate of a micro-state of emergency on a given territory - and because the CSP didn't necessarily have the strictest of control, atrocities occurred.
Just in case this is too vague, I'm going to use a modern analogy:
Imagine if Alexandria Ocasio-Cortez (AOC) or any member of "The Squad" (if you're USAmerican) or Rima Hassan (I know she's a European deputy not a French one but try to follow my analogy here, I'm struggling to find radical leftist politicians who actually get an impact so insert here any radical-ish leftist elected member of a legislative house). Imagine one of those, and they were sent to Iran (or Iraq and Afghanistan in a very close past) (and yes the fact they're women of color and some of MENA origin is actually very relevant in terms of social power struggle for the analogy here), and they could directly decide on battle plans, they could demote or promote any member of the military, and they had the power of life and death on not just regular soldiers but the generals themselves.
That's how fascinating a representative of mission was.
I don't know for AOC but I know for sure that if Rima Hassan had the power equivalent to a representative on mission in 1793-1794, she would be leading a war against Israel in the name of Gaza. (Remember, the Montagnards/Jacobins were actually, sincerely, genuinely leading a war in the name of Universal Rights against the "Coalition of Kings and Tyrants". It wasn't a hollow, cynical slogan hiding a need for oil or, in their case, wheat - though this did become a matter of debate when the armies started being victorious.) That's how much power they had to change the course of history. And that's why they were "terrifying" to the establishment.
Much cooler than just another military dude IMO.