Good quality adjustable dumbbells like the Ironmaster Quick Locks are the best. They are compact, have extensive weight combinations and are unbreakable. Cheap adjustable dumbbells will break eventually. Then you will buy Ironmasters.  Spin lock dumbbell handles, and Olympic Dumbbell handles do have their place. But they do have limitations. If you are on a tight budget and only need them for certain exercises, then maybe they are ok. However, they are not great for bench pressing which is a dumbbell exercise that is well worth adding to your program.  My advice is that if you can’t afford quality adjustable dumbbells, wait until you can. Spending money on cheap stuff is only going to set you back further from getting quality.  My Ironmaster’s have lasted me 20 years. I have done so much training with them. They are still going so they work out to be the best value gym equipment in the long run.