The Command squad has changed a bit since last codex. First, it’s no longer called an Honor Guard. I guess having a Space Marine Honor Guard with completely different equipment was too confusing. It is no longer unlocked by taking a character, and it now takes up an Elite slot. The Command squad still comes with a Sanguinary Novititiate, but it now also includes a Company Champion. While this does limit the squad’s flexibility a bit, it is a free upgrade (relative to the Space Marine Command squad). You start with a base squad with Feel No Pain, a WS 5 Marine with a power sword and combat shield, and 3 Veterans that you can arm however you want.
Command squads can take all of the standard dedicated transports, as well as jump packs. One Veteran may carry a company standard, if you’re worried about morale issues, and they can take any melee, ranged, or special weapons that you want. In the past, Command squads were usually loaded out with four special weapons to act as a specialized firepower squad. Now that they can only have three special weapons, this is less attractive. An Assault squad can carry the same number of special weapons (if you count the Sergeant’s pistol) for a much cheaper price.
Command squads can be armed for close combat, which makes sense since they already come with a Company Champion. However, their small size and lack of extra abilities mean that they will generally be out-performed by Death Company and Sanguinary Guard (you’ll hear this a lot as I review our assault units). They are separated from our other squads by their access to storm shields (shared only by Vanguard Veterans) and their access to special weapons (shared only by Assault squads). As storm shield carrying tarpit units, they outperform Vanguard Veterans due to the presence of the Sanguinary Novitiate and his Feel No Pain.
Unfortunately, Command squads don’t have much of a niche in our current Codex. They can still be equipped as a good assault unit or special weapons delivery squad, but other squads can perform those roles slightly better. Still, the Command squad is not outclassed enough that you will handicap yourself by taking one. They are a great squad for a dedicated painter that wants their army to stand out. Command squads also provide great narrative fodder; how you equip them says a lot about your HQ, and can really sell the backstory that you construct. While they’re hardly the most competitive unit, there are still lots of reasons to take a Command squad.