Legion Reconnaissance Squads were formed from experienced Space Marines expert in operating independently and often deep behind enemy lines. These specialised troops were the eyes and ears of their Legion in the field. For this task, they were armed and equipped with a variety of specialised wargear including long-range weaponry, sensory Auspex and stealth gear. They served as scouts and intelligence gatherers, identifying targets and gathering information on enemy movements and strengths. They also served their Legion as pickets, saboteurs, raiders and snipers where needed, and in open battle were experts in sudden flanking manoeuvres and infiltration attacks in support of their main force.
Basically, the Legion Reconnaissance Squad is your basic Space Marine Scouts, albeit better due to increased WS and BS. They cost about as much your standard Space Marine, hence upgrading these guys can prove to be quite costly. However, one can argue that they are probably one of the more reasonably costing unit, in comparison to the standard Codex. But really, who cares about the Codex Astartes. Only the pathetic and ignorant Roboute Guilliman and his so called glory Legion would abide (and create) such an absurd thing.
The Legions were and still are the most powerful armies in all of 40k!! Anyway enough of this, let's talk more about the Legion Reconnaissance Squad ay?
Many of the Legion Reconnaissance Squad's options are exactly like Codex: Space Marines.
Sniper Rifle - 3+ Armour Save with a Sniper Rifle, looks cool and sounds cool!! Just watch what you take, a 15 point Marine can easily become expensive with all these upgrades.
Space Marine Shotgun - Stick with the Bolter. Too bad Shotguns in the future are pretty weak.
Chainsword/Combat Blade - Unless you're Space Wolves, leave this at home, unless you have a plan.
Nuncio-Vox - Quite useful if you have a host of Barrage type weapons or perhaps Deep Striking units.
Cameleoline - Provides Stealth, so quite handy. Just watch your points.
Melta Bombs - Nice, but you have to take it for the whole squad so it becomes too expensive. Would've worked well if you could take it for a few models.
Recon Armour - You get Infiltrate and Move Through Cover if you do this, problem is your Armour Save is now 4+
Chainsword/Combat Blade - There are better options for a Sergeant.
Power Weapon - Power Sword or Power Maul, your choice. Power Axe would be nice, but I'd rather take the Power Fist.
Power Fist - This might actually be the best option, coupled with Artificer Armour. I might have read it wrong, but the Sergeant cannot take Melta Bombs.
Combi-Weapon - Your choice really.
Plasma Pistol - Too expensive!!
Artificer Armour - If the whole squad is armed with Recon Armour, and the Sergeant takes this, he still gets Infiltrate and Move Through Cover. It's a win in my book.
Stick these guys in cover and shoot things. There are better units for the Support Role, but hey, thematic is a win!! As long as you're having fun!