The adjustable dumbbells you buy from eBay, Amazon and Argos can be cheap and nasty, but they do the job.
A cheap set of 20kg normally comes with 2 handles and the ability to load 10kg on to each. Sometimes you can load all the weight onto one handle:
The weights come in either metal or cheap and nasty vinyl. Both are ok, so its down to your budget.
Ive seen adverts for 20kg sets between £23-35.
If you are building a home gym, obviously you can up the budget and buy cooler nicer ones, but the cheap adjustable ones do the job. If you can bicep curl them, triceps extend, press, goblet squat, thruster and use them in lunges or step ups you have a really useful tool that can be pushed under the bed or dumped in the garden.
The circular spin lock will always, (always) jiggle loose and its a pain to keep on tightening them. Its a first world problem.
I bought my set from Decathlon in Canada Water, but discovered that it was quite a job getting them home on the tube.
Interestingly almost everyone I see seems to have a 1kg dumbbell at home. There must have been a really persuasive advert that I missed!
The reality is that strengthening and building your physique, or just developing fitness, requires a regular increase in load. If you can bicep curl 1.25kg, soon, you need it to be 2.5kg. If today you can only lift 1kg, quite soon, you’ll need to buy a bigger weight, so I’d opt for the cheapie adjustable set.