I'd been deliberating about buying a set of these for years. I just wish I'd purchased them sooner! I also purchased the stage 2 & 3 expansion kits, and having 180lbs/82kg in such a small and compact block is ideal for my current living environment. They fit nicely under the bed :-) Before, I had around 60-70kg of various plates, bars, spinlocks etc. that took up so much space. So I sold them all to help contribute towards the purchase of the PowerBlocks.
They aren't cheap; but they are a solid and worthwhile investment. I was a little hesitant because I thought they looked clunky and 'un-dumbbell' like, so may find it awkward to use. But upon arrival I was surprised by how compact they were - even with the 2 & 3 expansion sets added. They were no bigger than standard dumbbells with regards to length, which was my main worry. You dont want them clanking together or restricting full range of motion when doing chest presses or shoulder presses for example. These are no problem whatsoever. Have you ever seen a 40kg hex dummbell? These are more compact than those.
Changing weights is super quick, although you need to be a little be careful with the pin selector to ensure it goes into the right slots/level i.e. inserts/exits on the same level. Which can happen if you decide to lifts weights when drunk ;-)
I was also a bit concerned that they may be super noisy, due to moving parts or the adder weights within. But they are no louder than general spinlock dumbbells with iron plates. The adder weights can move a little bit if you are swinging them around doing snatches, cleans etc. But's they have little rubber cushions on the end which reduces the noise which is good.
They are really well balanced too. When you see videos or pictures, you can't envisage using them the same way you would standard dumbbells - they look odd. But literally on my first session using these I forgot. Your muscles don't care what they are lifting - they just need resistance.