The Land Raiders all work on the same chassis, with AV 14 all around and 4 HP. All of them mount two sponson weapons and a forward facing gun, as well as having the option to stick a multi-melta on top (you should always do this). Land Raiders can carry Terminators, making them and Stormravens our only options for transporting Terminators. They all have the rules Assault Vehicle, making them our best way to deliver assault units, and Power of the Machine Spirit, allowing them to split fire with their many weapons. There are three patterns of Land Raiders with different weapon loads and transport capacities.
The Land Raider Phobos (the standard Land Raider) has a twin-linked heavy bolter and twin-linked lascannon sponsons, and it has the smallest transport capacity at 10 models. The Phobos often gets a bad reputation for being a confused unit. It has long-ranged weapons but wants to deliver its passenger into assault. I’ve said this before, but it is really missing the point. There is really no downside to having the extra range. Consider the Phobos when you want your Land Raider to destroy enemy vehicles; add a multi-melta and it can happily put strong shots into two enemy vehicles each turn.
The downside to the Phobos is its small transport capacity, only able to carry a minium strength Terminator Assault squad. As such, the Phobos isn’t appropriate if you’re trying to mount a serious assault force.
The Land Raider Crusader has a twin-linked assault cannon and sponson hurricane bolters, making it excellent at scything down light infantry. It has the largest transport capacity with 16 models, and has frag assault launchers, meaning that units assaulting from it count as having frag grenades.
Overall, this makes the Crusader the most dedicated Land Raider for launching an assault. Its short range firepower will thin out the infantry that could overwhelm its elite assault unit, which can be quite large due to the high transport capacity. Fill up the Crusader with Assault Terminators or Honor Guard and possibly a few characters and send it straight at the enemy, and you’ll generally come out on top.
The Redeemer fills a similar role to the Crusader; it carries the same twin-linked assault cannon and frag assault launchers and has sponson mounted flamestorm cannons, which are brutal with S6 AP3 templates. It has a reduced transport capacity of 12 models, but at least it can carry a Terminator squad with an attached character.
The Redeemer fulfills the same role as the Crusader, just with a smaller squad and a predilection for killing heavy infantry. I personally prefer the Crusader because I like the extra range on the bolters compared to the flamestorm cannons, but the Redeemer is still a good option. It just requires more careful placement to maximize the damage the templates cause.
Sergeant Chronus is a rather expensive upgrade for a single Ultramarines tank in the army. He does add to his tank’s durability with It Will Not Die, its reliability by ignoring Crew Shaken and Stunned results, and its hitting power by making it BS 5. If his tank is destroyed, Chronus will hop out and act as an Independent Character Veteran Sergeant.
All in all, Chronus does a lot for a single tank but you pay a lot for it. I think he’s best used in a Land Raider, where his rules will keep it alive longer thanks to an extra hull point and the ability to ignore Shaken and Stunned results will help it deliver its cargo. Honestly, I doubt that his points cost is justified for any Space Marine tank, but if you have a single tank that is pivotal to your battle plan, than put him in it.