The "serious business" Chaos Codex review begins with the one unit in the book that is outright better than it's vanilla counterpart, the Rhino. I don't think I need to go into the benefits of "meching up" on this site (Kirby et al have explained far more eloquently than I care to). I also don't think I need to go into the specifics tactics of using transports (spoiler aler, it involves trains, V formations and 1" gaps). You'll have to trust me when I say that you want to bring transports if you can, and the humble Rhino is all the Chaos Space Marines get. What I will discuss is why the CSM Rhino is superior to the vanilla Rhino and how you should be bringing yours.
There are two different ways a transport enahnces your army. The first, which I like to think of as "old school" 5e is providing mobility and protection for your (usually scoring) units and cover for the rest of your army. In this respect, the vanilla Rhino performs admirably. The second, which I think of as (wait for it) "new school" is providing threat of tis own, ie the "1+1." The vanilla Rhino simply cannot do this. A stormbolter is a fine weapon when a squad has 5 of them. On it's own? I'll pass. A single shot krak missile is also a fine weapon, but it is really only valuable as an alpha strike weapon. Many, if not most, Rhinos will be zipping up 12" and popping smoke turn 1 (and likely turn 2 if you know how to choo-choo). By the time your HKs fire turn 2 and 3, the effect is diminished. The HK seems tailor made for las/plas Razorbacks who will likely be standing still and targetting light armor turn 1.
How about the CSM Rhino? Well obviously, it can perform the old school role just as well as the vanilla Rhino as they are both 11/11/10 tanks with the same doors and firepoints and the same repair rule. The Chaos Rhino starts to shine when you start thinking 1+1. The 10 point combi-weapon is a very good weapon on a transport. First, there's the combi-melta. In your head, a 1 shot melta may not seem like much, but try to imagine it on the table. Think about an empty Rhino with a combi-melta. Are you going to shoot at it? Waste precious suppression fire on an empty, 45 point transport? What is it's within 12" of one of your heavy support tanks? Or one of your transports trying to break out to seize an objective? Or a MC with a rapidly diminishing number of wounds? Now you start to pay that Rhino some concern. You start make choices. And that's really all we can do as players. Force our opponents to make difficult decisions and hope they choose wrong. A simple combi-melta does this. Amazingly, the combi-flamer may be better. One of the things that separates average players (me) from good players (Kirby) is the ability to effectively utilize tank shocks. Tank shocking allows you to arrange your opponents models into a formation that is more beneficial to you, often a "template me" formation. Unlike the vanilla Rhino who shocks and lets his buddies do the killing, the combi-flamer Rhino can perform both roles, allowing your shooty units to focus on other things. I know a flamer isn't particularly scary to marines, but it terrifies guardsmen and dark eldar and orcs. A combi-weapon Rhino provides a solid, affordable +1.
The Chaos Rhino's other weapon option (yes, I'm ignoring the combi-bolter and the combi-plasma) is the Havoc Launcher. I think this is an underutilized option. Twin-linked s5 small template with 48" range. In the early game when foot units are spread out, a small blast is pretty crap. However, we already discussed that Rhinos want to be moving a smoking in the early game. What about mid and late game? Now foot troops tend to be more clustered. They have disembarked and are arrayed around their transport, or they are huddling in the wrecked of an exploded transport or they're bunched up after a consolidation move or they've been tank shocked into a nice cluster. Now a small blast starts to gain some value. I think over the course of a game, the havoc launcher is probably as effective as the TL Heavy Bolter on top of the standard Razorback that seems to be making a combeack. For 10 points more than a standard RB, you get a larger transport capacity (which you may or may not use) and a top hatch (which you will definitely use). The Havoc Rhino will never be as good as the Razorback at standing back and shooting and you probably won't be bringing a lot of empty ones. However, for pushing units into midfield and across the field, I think the Havoc Rhino is a very effective choice.
So, in summary, the Chaos Rhino is a good unit (don't get used to hearing that is the Chaos Codex Review) that plays a key role in supporting your army. A standard list will bring 4-6 of them to ferry your troops around and "Rhino spam" lists are very possible, bringing up to 12. You can equip them 1 of 3 ways, with a combi-melta to add some AT, with a combi-flamer to add some anti-troop and maximize your Tank Shock threat, or with a Havoc Launcher to provide solid mid-late game anti-troop and some much needed range.
