I’m a bit surprised at some of the comments above regarding adjustable dumbbells. I’ve worked out at home for the past six years using adjustable dumbbells for most everything, and wouldn’t have it any other way.
There are two things, IMO, that make adjustable dumbbells superior to fixed weight ones when training at home. First, for a complete and effective workout, one needs a wide variety of resistance for different exercises; second, small increments in resistance are mandatory for progressive, safe strength training.
Suppose you plan to do bent-over DB rows for your back and biceps, DB bench presses for your chest and triceps , Goblet squats for the lower body, DB upright presses for your shoulders, traps and triceps and lateral side raises to finish off the shoulder area. Each of the exercises needs a different weight dumbbell, from maybe 15 lbs. for the lateral raises to 100 lbs. for the DB rows and all sorts in between for the rest. And to keep things going, you’ll need to be able to add a single pound to the side raise weight every now and then but five pounds to the rowing weight.
I don’t really see anything less than a massive rack containing dozens of different-size fixed-weight DBs covering the need for an effective workout. If I was a millionaire, I’d have that. Now, I’ll just use three pairs of cheap dumbbell handles and a plastic box full of weight plates ranging from a half-pound to 20 lbs. These I can mix up every which way for any need. About 90 % of what I have was bought second-hand, as new sets are ridiculously expensive, as others have noted.
Failing to twist the screw locks on tightly on cheap adjustable dumbbells before hitting the iron is a recipe for injury and dented floors. Since learning that, I haven’t had any issues with mine.
All the weight plates I have are cast iron. I hate the way rubberized (or worse, vinyl) weight plates look, and at least cheap rubberized ones sometimes have a rank smell, as well. To keep floors intact, I have a piece of MDF under my weight training corner, covered with a heavy mat. The best dumbbell handles I have are all plain iron. IME, rubberized handles tend to break down with heavy use. I’ve never experienced hand problems from gripping the plain iron handles of up to 120 lbs. dumbbells without gloves.