I find them great to be honest, Not as good as a set of fixed DB's, but not $6K either...
Much better than spinlocks as they stay locked on and have a flat end for setting them on your thighs as you get them into place for benching.
Not slow to change, but not ultra speedy either, particularly as you cross the original 80? lb max and use the 120lb extension for weights from 80-120 (ie changing from say 70 to 90 lbs per DB is relatively slow, but not horribly so.
They are really solid and well put together, and in particular if you are currently lifting less than the starter kit goes to, then a great option.