@gregory_r_g Generally you don't expect any decent kettlebell to break and there won't be much wear and tear either, so you should ideally get the right kettlebell for you the first time.
With cast iron bells the bell and handle will often be painted or coated (powder coating or something else). If you use 1 kettlebell at a time I don't think you should worry (my oldest painted cast iron is around 10 years old and still has unbroken/unchipped original handle painting (not powder coating). If you use 2 cast iron kettlebells at a time then you will likely have them bump into each other, either while swinging/cleaning both kettlebells or when you hold/catch them in the rack position. I think over time the repeated bumps will cause "damage to the paint of the handle (Maybe someone else knows better for powder coating?) and make the handles less smooth. You can fix this by either sanding away any painted problem area or you can work on repainting the handle as you wish. The iron of the kettlebell itself will be fine, but I suspect the finish of cast iron paint/coating will wear down and start chipping with time and repeated bumps.
I have no experience with neither KettlebellKings or adjustable kettlebells, but most of my kettlebells are standard competition kettlebells and therefore are more or less the same as the kettlebellkings one without being adjustable. I SO MUCH MORE prefer the design of competition kettlebells because to me they are more comfortable to hold and the size feels "right" for both singles and doubles. The size remains the same with all weights which is good for mastering technique and balance, whereas with cast iron the size changes and you have to make readjust every time, though it isn't difficult to adjust. The width of the hanle on competition kettlebells is smaller than most cast iron bells which makes gripping the bells easier. Also usually the handles of competition kettlebells are steel and therefore won't have any chipped paint or other wear over time, though the bell itself will usually be painted and can chip there, but this is to be expected when you start doing doubles.
I bought my kettlebells before I heard of adjustable ones. I really like the idea of it in terms of both space saving and money saving. If it is durable just like regular competition kettlebells then I would be tempted to buy 1 or 2 because of the good variety in weight they offer. The major downside is that you have to open the bell and remove plates every time you wish to change weight. I think I would get used to it, but since I train GS / kettlbell sport I tend to do warm ups by doing the same movement with lighter bells and build up to my training weight and afterwards I sometimes do extra sets with lighter bells again for extra training volume. This would make me change the weight 3-5 times easily (or 6-10 times since I use double) for most of my training sessions. But I would have the opportunity to train with 21,22,23 kg and 25,26,27 kg instead of only having the option for 20, 24 and 28 kg (I lack bells in smaller weight increments)... Overall I think adjustable looks very attractive, especially if these will be your first kettlebells. The only major downside being the time it takes to change the weight (hopefully not too long?) and possibly worries if the durability is lowered because of the more complex construction?
