I don't use them per say, but I sell them. I think they work just fine. However, ours are 20" long compared to 14" for the standard bells. 45lb plates may look awkward on there, but I don't see them being any less functional.
If I was going to start over on dumbbells I'd buy powerblocks off Craig's for the lighter then look for a good deal on heavier dumbbells also on Craig's. I wouldn't mess with clips or locks or anything that would consume the least bit of time or hassle during training.
I bit the bullet for some powerblocks this summer and couldn't be happier. They are expensive when you get into the heavier but I got mine on sale, U-90's for $500 and change. I still use my OLY DB handles but only for heavy pulling exercises, I don't want anything directly over my head held on by a spring collar.
I priced a set of fixed dumbbells and they are cost prohibitive. I brought the olympic dumbbell handles and just load them up. Works fine. With the 25s you can reach 150lbs and more easy. It can get unwieldy with 25's but they are the best alternative in my opinion. Not sure how many 10's they could handle and if this would be better as my 10s are limited.
Really, it's a lot easier to change weight on a barbell than it is a dumbbell and I'm thinking the quickest type of dumbbell is not going to be all that secure.
Never the less you are hot on the trail of my laziness. In my gym I have 3 barbells and a trap bar. The trap bar and the barbell that is alway on the floor are both always loaded with starting weight. One bar is always in the cage ready for squats and the other is on the outside of the cage ready for anything.
You probably missed the thread a few years ago, but I basically went into orgasmic seizures when I got my rolling plate holder (that's right, rolling fucking plate holder). All I need now is one of those lever bars for lifting a bar off the floor to load and unload plates.