A lot of the stuff you can replicate with a dumbbell. But a lot you cannot. You can use kettlebells pretty uniquely for all sorts of disadvantage leverages that will make them ‘harder’. Turkish getups for instance. They’re also better suited for lateral raises, and have interesting balance with your pressing. Doing presses bottom up style can effect your grip positively as well.
They’re a great tool.
That said, for specifically building STRENGTH. They’re not the BEST tool for the job if you only have one pair. You need progression if you intend on getting stronger.
Keep in mind that we all define strength differently. And perhaps you can improve by going up to higher reps, or doing more sets. Whatever. After a while you’re going to plateau just because you can’t get any heavier… Point blank period.
Once you get past 8 reps you’re really not building the kind of strength we’re talking about that is really conditioning.
But kettlebells are one of the best tools you can have for conditioning. A jump rope, somewhere to sprint and some kettlebells will get you in top notch form. Add in a pullup bar and you don’t need much else.
Since you’re a beginner that program is a great place to start… There are other, better programs that you will need to progress onto after though because you’ll get all the usefulness you can out of that program in a few months time. 5x5 was designed for progression. 5x5 with set non adjustable kettlebells is kinda ass backward.